Are Index Funds Making the Market “Irrational”?

In this episode of Motley Fool Hidden Gems Investing, Motley Fool contributors Jon Quast, Matt Frankel, and Rachel Warren discuss:

• High bandwidth memory for AI.
• SK Hynix’s U.S. IPO.
• What happens with ETFs when companies go public?
• How ETFs and index funds influence markets.
• Rational vs. irrational stock prices.

To catch full episodes of all The Motley Fool's free podcasts, check out our podcast center. When you're ready to invest, check out this top 10 list of stocks to buy.

A full transcript is below.

This podcast was recorded on July 6, 2026.

Jon Quast: Are index funds making the market irrational? You're listening to Motley Fool Hidden Gems Investing. Welcome to Motley Fool Hidden Gems Investing. I'm Jon Quast, and I'm joined today by Foolish contributors Matt Frankel and Rachel Warren. Before you dive into today's episode, do yourself a favor. Head over to news.fool.com and sign up for Breakfast News. It’s a free daily email from The Motley Fool, landing in your inbox by 7:30 AM every morning, packed with the stories long-term investors actually want to know about.

We're going to tackle some topics today on today's show. We have actually two topics about ETFs from our mailbag. Something like that you wouldn't necessarily find in Breakfast News, but you might find something in breakfast News similar to the story we're leading with here, and that is the topic that we have regarding SK Hynix. Now, SK Hynix is a computer memory company based in South Korea, and it's already publicly traded there in South Korea. But as early as this week, it does plan to list some American depository shares here in the U.S. or ADR. It's going to trade under the ticker symbol SKHY, and it's targeting to sell nearly 178 million ADR shares. That will hopefully raise roughly $28 billion. It needs some money to build new factories and furnish them with chipmaking equipment. Now, one could say with AI, GPUs aren't holding anything back. It's the computer memory, finding specifically that high-bandwidth memory. That is what these companies need right now. That is what we are not making enough of. My first question here to you, Rachel, is what exactly is high-bandwidth memory, and who makes it?

Rachel Warren: High-bandwidth memory or HBM, as it's commonly known for short, that's basically the ultimate data superhighway for artificial intelligence. Traditional memory chips sit far away from the computer processor. That is creating major data traffic jams, particularly in the age of intensive AI applications with memory aims to solve this by stacking memory chips vertically like a skyscraper, if you will, and placing that entire stack right next to the main processor. This lets massive amounts of data travel, in some cases, up to 10 times or more faster while using way less power.

In short, we're at a time where AI processors are constantly starved for data, high bandwidth memory is the only memory fast enough to keep them fed. Now, right now, making these chips, it's so complex. It's so expensive. There's only three companies in the world that control this entire market. SK Hynix is the undisputed king of the mountain of this space. They command over 50% of the market as the primary memory supplier for Nvidia's AI chips. Now, the other two players are Samsung, global memory giant, also based in South Korea, and Micron, the only major player based in the U.S. Because building these high-tech factories requires billions and billions of dollars, SK Hynix is coming to Wall Street to secure the cash they need to stay ahead in this very intense race.

Jon Quast: I think that so many investors missed the whole memory trade because historically, memory is such a commoditized market, and there are so many fears related to historic patterns when it comes to this commoditization. But right now, it is enjoying these companies, specifically SK Hynix, enjoying these incredible business economics. I would say it's very smart for it to capitalize on the trend right now, go public here in the U.S., raise that capital that it needs. It's good IPO timing, no doubt. I am curious here about long-term shareholders. Do either of you think that SK Hynix is a good investment when it comes public, or are you looking at that $28 billion that it's going to be raising and saying, maybe there's a secondary beneficiary here because that money is going to go somewhere?

Rachel Warren: There's no denying that SK Hynix, they're riding an incredible wave and timing this U.S. listing during what is essentially peak AI euphoria. I think it's a brilliant move from a corporate perspective. Now, I am not planning to buy shares at any point in the near future, and my hesitation comes down to a few things. Obviously, there's capital intensity, but there's also a long-term cyclical risk. I mean, building and equipping these facilities requires an astronomical amount of cash, as I was discussing. As a shareholder, my concern is that buying in today means you're betting that AI demand will remain hot enough for long enough to absorb all this new capacity. Even if it does, there is a lot of excitement that's baked into the stock right now. I prefer not to buy newly listed stocks straight out of the gate. I understand SK Hynix is listed internationally.

Now, if as SK Hynix is deploying billions into infrastructure, a massive portion of that capital flows directly into the order books of a lot of companies, including the semiconductor equipment giants like ASML, Applied Materials, and research. Those are companies, those are equipment suppliers that essentially get paid to furnish and tool these factories upfront. That's actually much more where my interest personally lies. There's significant revenue backlogs that are really locked in, regardless of whether the memory market faces some a supply glut a few years down the road. For me, I'm more interested in capitalizing on that guaranteed capex, but I certainly see that there will be many investors that are primed to buy shares of SK Hynix.

Matt Frankel: I'd add a few things here. First, I'm not surprised at all to see this listing. In fact, I'd argue that it would be irresponsible not to raise capital through equity sales at these levels. Micron's valued at over $1 trillion. I think they should raise more capital if they need it. Having said that, you won't see me buying SK Hynix or Micron at these levels anytime soon. Rachel's right that the equipment suppliers are really the play to watch. But I really don't put all three of them in the same basket. Specifically, ASML is the only company that makes those EUV lithography machines, and their orderbook is already stretched out for years. It's not just a memory-specific play. Whatever the industry is doing in a few years, it's going to be fine.

On the other hand, Lam Research is much more of a memory. That makes up more than half of its revenue. I'm a little bit more concerned about that long term, especially if this remains a commoditized business. Applied materials I put in the middle ground. It's got a very diverse revenue stream, great demand, not terribly levered to the memory business, but it's not exactly a monopoly like ASML has. The equipment names aren't exactly immune to cyclicality. Look at 2023 when all of the memory companies that we mentioned cut their capex around the same time in response to slumming demand, all the equipment makers took a big debt. If AI is truly a structural change for the memory industry and reduces the cyclical nature of it, all three of them could be big winners, but that's still a very big if at this point.

Jon Quast: Well, based on my portfolio, I think I'm taking the bet that it's an I and hoping that this continues to be a structural change in the market. Well, after the break, we're going to dive into the mailbag. Looking at some interesting ETFs that have to do with private companies, you're listening to Motley Fool Hidden Gems Investing.

Welcome back to Motley Fool Hidden Gems Investing. I'm going to be honest, the news over the weekend was pretty thin, but I'm actually pretty thankful for that because it does allow us to double-dip into the mailbag today. First up here, we do have a question about some ETFs. I'll just read it as it is. Now that SpaceX has debuted and other AI companies are close to IPO as well, what happens to ETFs that hold shares of these companies after they go public? I know that XOVR and VCX and other ETFs hold pre-IPO shares of one or more of them, but have they stated whether they will hold them for the long term or flip them when possible? Since SpaceX had a nice pop, but is now settling down, is one just better off avoiding the ETFs and trying to buy the shares directly, if one believes the narratives. To me, the listener is basically asking about ETFs in general, but also mentions two ETFs specifically. The ones that he mentioned specifically are ER shares, a private public crossover ETF, and the Fundrise Innovation Fund. But I think we should mention before we go any further, that those two ETFs, they're actually not quite the same thing. There are some differences that are important to point out.

Matt Frankel: Yes. The biggest differences, one just between these in general and standard ETFs is that they invest in private companies, alongside some public ones. The XOVR, which is the ER shares private, public crossover ETF, a tongue twister. It's a traditional ETF. It happens to own private assets alongside a portfolio of mostly publicly traded stocks. I think a 15% cap is what they set there. I think companies like Nvidia, Palantir, etc, those make up the bulk of the fund. On the other hand, BCX, the Fundrise Innovation Fund. That's actually a closed-end fund that is much more weighted toward private companies. It's also not a liquid ETF, meaning that it has quarterly redemption windows when you can sell shares if you want to, and even those are limited, there's no real secondary market for the shares. It's really tough to cash out whenever you want to.

The bottom line is that the ER shares private-public crossover is the better option if you want to be able to readily cash out of your investment when you want to. But if you really want more of a concentrated play on private companies, that Fundrise Innovation Fund is the way to go. It's important to note that they're not really interchangeable products. Like any ETF, you should read the prospectus. But in this case, it's really important to know the differences, know what each one holds, and know the fee structure of each one because they're somewhat different and somewhat complicated in the Fundrise Innovation Fund before you decide to invest in either.

Jon Quast: Imagine buying into one of these things and not knowing that you can't sell when you want to. That would be a really important thing to know. But now we move on basically two questions here from the listener. The first is, will these ETFs keep holding SpaceX long term, the ones that invested before the IPO, Rachel?

Rachel Warren: To address that question, the answer is generally, yes. Matt did a good job of explaining how these funds are going to handle things a bit differently when it comes to SpaceX. Now, ER Shares has stated that they view SpaceX as a long-term conviction holding, and they did the exact same thing, essentially with a company like Klarna. They held shares through its public listing. Now, similarly, the Fundrise Innovation Fund operates similar to a public venture capital fund, and their goal is to back the structural tech giants for the long haul. They will essentially continue managing SpaceX as a core holding within their broader portfolio.

Matt Frankel: It's also worth noting that there are post IPO lockups that restrict insiders, pre-IPO investors from selling for a specific time period. With SpaceX, it's seven different tranches that the lockups expire. It's really nonstandard, and it's really not that long of a podcast to go through all seven tranches and when they kick in. But the thing to note here is that lockup periods can apply to ETFs that hold these shares as well. If they hold them before they were public companies, then they become public, and that's to prevent if an ETF owns, say, 2% of a private company that they immediately dump that when it becomes public and collect a windfall. Keep that in mind as well when you think about whether or not and when these companies can sell.

Jon Quast: If you're wondering why it matters whether or not an ETF holds shares of a company or not, we're going to tackle that more in our next segment. But before we move on, I do want to hit the second part of the question here from the listener, and that is, should one invest in these ETFs or just buy shares directly once they go public? I will say specifically with the XOVR ETF, that helps investors buy shares of companies before they go public. The underlying premise of the fund, once a company goes public, it seems like that you don't need that anymore because it is available publicly, but I don't know. Matt, any comments to add?

Matt Frankel: Jon, the short answer is, I wouldn't buy either of these specifically for SpaceX exposure. Even if you don't want to own the stock or even if you don't want to own the stock directly, but want to own it, there are easier ways to go, especially now that SpaceX is officially part of the NASDAQ-100, and therefore will be added to much lower-cost ETFs that will track it and will be pretty concentrated in it. But these could be a good way to go if you want SpaceX exposure and that private company investing all in one place. The two funds there's something an individual investor would really have a tough time or an impossible time replicating on their own. My general thought is that if you have a very strong conviction in SpaceX, just buy the stock directly, save yourself the fees. If you want exposure to SpaceX and other big tech companies without owning them directly, I use this to get exposure to Nvidia, for example, use a NASDAQ-100 fund or something similar. If you want the public and private company exposure all in one, decide which of those two ETFs best meet your needs and go from there. You really have to decide which of those categories you fall into.

Rachel Warren: I think that's right. Personally, SpaceX is not a stock I'm interested in investing in, at least not at this point in time. I won't deny that the company's achievements are historic. The capex is required to move forward on a lot of Musk's goals remain astronomically high. I think the regulatory hurdles are constant. Also the path to consistent profitability is another element that worries me. I will say funds like XOVR and VCX, those are really diversified portfolios. If you are an investor that tends to put cash in the public markets, but you also want that exposure to those very highly anticipated names that could be going public in the next year or two, OpenAI, Anthropic, that can certainly be a good way to go to have some exposure in your portfolio there. Now, for SpaceX, if you believe the story behind the business, if you want exposure to the stock, that diversified approach could also work. Now, for me, the high execution risks mean I'm staying on the sidelines for this one, but watching with a lot of interest to see how the stock performs in the next year or two.

Jon Quast: Well, if you're still wondering about ETFs after the break, we're going back into the mailbag to talk about potentially how they might move markets in irrational ways. You're listening to Motley Fool Hidden Gems Investing.

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Jon Quast: Welcome back to Motley Fool Hidden Gems Investing. On a quick note, you can send us questions like this to podcast@fool.com. We love to take your questions when they're Foolish, when they are short enough to read on air, send them in. If you have a question for Rachel, Matt, or myself, anyone on the show, keep them Foolish. Podcast at fool.com, podcast at fool.com.

Our second question from the Mailbag today goes like this. I'm a data analytics professional working in the co-op energy field. I enjoy trying to apply analytical thinking to the market, but it's not my expertise. I listen to The Fool podcast daily as I commute in my EV, there is persistent talk, U.S. equities, specifically S&P 500 being overvalued. I would really like to hear experts talk about expected retirement liquidations versus actual retirement liquidations by generation. My hypothesis, if there are more net holders of equity and a growing passive investment into the same equities, thanks to ETFs, 401(k), etc., would we not expect behavior that is irrational because of structural shifts, not actual human choice? Thanks.

Here's what I like about this question, guys. This person is admitting that they are not an expert, but that is OK. You do not have to be an expert to be an investor. Really, he's dialing into this analytical instinct here that he has as an individual investor. He's saying, look, I feel like maybe there's a structural shift happening in the market, but some people are talking about it like it's an emotional shift. Trying to understand the difference between structure and emotion, I really like the instincts here. Rachel, what do you think?

Rachel Warren: I think the listener’s instincts are spot on, and it also shines a light on a reality that I think a lot of traditional models ignore. We'll see, for example, overvaluation in the S&P 500, but that isn't really retail FOBO or investor greed. A lot of it goes back to a very mechanical reality of a fundamental change in how the stock market works. Every two weeks or so, millions of paychecks are automatically swept into 401(k)s and passed to ETFs. The computers running these funds, they don't care if a stock is cheap or ridiculously expensive. They are programmed to essentially blindly buy the index. Now, because the biggest tech giants are the most heavily weighted, the lion's share of every automatic dollar tends to get funded right back into those exact same companies. That can also naturally inflate their valuations regardless of human choice or individual investor appetite.

What's interesting is that a lot of the old economic models assumed that when baby boomers retired, that they would immediately dump their stocks to buy bonds and cash, which would naturally deflate the market. That has not borne out. In fact, modern retirement structures have turned them into what we would call permanent net holders, about the top 10% of those in the baby boomer generation hold over 70% of that generation's wealth. These wealthy retirees, they don't need to liquidate their stocks. They are just letting them ride, passing them down to their kids, their grandkids. When you can bind that wall of automated passive inflows with a generation of retirees with significant disposable income who are not selling their stocks generally, you do get a market that behaves in ways that might look irrational to traditional value investors, but there's a very good reason behind the movements that we're seeing.

Matt Frankel: Let's add some numbers behind what Rachel just shared. Passive index funds made up less than 10% of all U.S. equity funds back in the ‘90s versus about 50% today. Because of this, it's now estimated, and things like algorithmic trading and programmatic things that they do on Wall Street, it's estimated that about 60% of all trading volume is now systematic and not discretionary. The listener is absolutely right. The old 4% rule, it made certain assumptions that retirees would sell their equities, cash out, go to bonds.

A lot has changed since then, as Rachel referred to as modern retirement structures, RMDs, for example, now start at 73, that's significantly later than they used to start where you have to start taking money out of your retirement account. Wealthy retirees, they often withdraw only what they have to, and more estates are now being passed to heirs with stocks that are getting stepped up basis and are never withdrawn or sold at all. Passive investing has created this self-reinforcing loop where passive money flows into the market but not really out as much. The biggest stocks go up; they become an even bigger share of the index funds. The next passive money in creates even more concentration, and this cycle repeats and repeats and repeats.

I push back that the market isn't behaving irrational here, but the behavior, it's a rational response to that new reality that we're talking about. One thing I'd watch out for is if the passive flows ever went negative, which could certainly happen and has happened in things like deep recessions, the same passive mechanics that caused inflated prices in the first place could deflate them using the same exact mechanism. We saw this during the initial COVID crash. That was a lot of that was attributed to algorithmic trading. It's not the discretionary traders that are driving prices up, but that could also drive prices down.

Jon Quast: What I hear you saying here is that yes, maybe perhaps ETFs and index funds have changed some structural market behavior compared to 30 years ago or 50 years ago. Things are quantifiably different now. My big question here is, if that's true, what do I have to do as a DIY investor? Do I need to change things? Do I need to be a rational investor as opposed to what I'm seeing a irrationality, or maybe we even need to define what does irrational even mean? Rachel, I'm going to let you go first here with this big question. What do I need to do?

Rachel Warren: In traditional finance, a rational "stock price" would reflect a company's actual business fundamentals, like revenue and earnings. Now, passive investing flips that on its head because it's very predictable. You've got the computers, obviously, the algorithms that are managing these flows. They're not analyzing balance sheets. They're matching market weights. That can and does create a distortion where the biggest companies at the market get the most money simply because they're already big. That can really untether stock prices from actual corporate performance. I do want to underscore that.

Now, does this mean you need to change how you invest? Obviously, we can't give personal investing advice. But for most of us, and those of us certainly here with the Motley Fool, it really means doubling down on that philosophy of long term diversification. Instead of letting passive flows trap us entirely in a few top-heavy mega caps, it's really important to build a robust portfolio of 50 or more high-quality individual stocks across different industries. Buying individual companies allows us as investors to really look at the underlying core business fundamentals that those algorithms ignore.

Now, that said, not everyone has the time or the interest to manage all those individual stocks. That's completely understandable. But this is something that can be adapted to individual investors, whether you're using equal-weighted index funds or actively managed funds as your core foundation. But I think the key takeaway is ensuring that our portfolios are truly diversified so that we're not entirely exposed to the whims of a few of the biggest companies in the world.

Matt Frankel: Jon, you had mentioned that we might want to define irrational here. Let's do that. Let's take a step back and define what that means. It means that in investing, irrational means that a stock — its price is disconnected from its underlying business fundamentals. It doesn't mean that it's expensive, it doesn't mean that it's cheap. It just means that the price doesn't go with its underlying business. A stock that's trading for 100 times earnings or 40 times sales could be completely rationally priced if the growth justifies it. I'd argue that passive flows aren't really irrational or rational. Rather, they’re indifferent to price, which is arguably more dangerous, that self-sustaining loop of passive money flowing in and driving the biggest stocks up. That can really have an interesting dynamic. I'd also say the passive flows that we're talking about don't really move the market much on a day-to-day basis. The volumes rather smooth and continuous. It's not like the Vanguard S&P 500 index fund is putting $1 trillion to work like today. It's a very continuous motion. Over time, they certainly can make a difference.

There have been studies done, Mega Cap performance in the passive era, which is what we're in now is more dramatic than it was a decade ago, even when you consider the changing fundamentals. Obviously, Nvidia is stronger today than it was five years ago. You can certainly tweak your investment strategy because of this. That doesn't mean trying to time the market because of what passive indexing is doing. No. 1, be aware of the concentration risk in your passive index funds. That's a big tweak that I've made. An S&P 500 index fund isn't the diverse investment it was 10 years ago. I expect a longer payoff period when you invest in deep value stocks, which is a big focus of mine. Passive flows, they affect the large caps most. It can create opportunities for long-term patient investors in things like small caps and international stocks. Periodic rebalancing is more important than ever when passive investing can push certain stocks higher regardless of their current valuation. Those are just some of the tweaks that I've made to my own investment strategy over the past, say, 10 years or so. Take those for what they're worth.

Jon Quast: Well, I think it's important for all of us, Foolish investors, to never push away from growing as an investor because there's always something that we can learn to improve for the future long-term health of our portfolio. That's what I'll be doing. That's all the time we have for today's show. Thank you so much for listening.

As always, people on the program may have interest in the stocks they talk about, and The Motley Fool may have formal recommendations for or against, so don't buy or sell stocks based solely on what you hear. All personal finance content follows Motley Fool editorial standards and is not approved by advertisers. Advertisements are sponsored content and provided for informational purposes only. To see our full advertising disclosure, please check out our show notes. Thanks to our producer, Dan Boyd, and the rest of The Motley Fool team for Matt, Rachel, and myself. Thank you so much for listening to our show today, and we will see you again soon.

Jon Quast has no position in any of the stocks mentioned. Matt Frankel, CFP® has positions in Vanguard S&P 500 ETF. Rachel Warren has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends ASML, Applied Materials, Lam Research, Micron Technology, Nvidia, Palantir Technologies, and Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.