The S&P 500 Just Hit a Record High. Here's Why History Says It's Still a Smart Time to Invest.

Since 2001, throughout my adult life, I've never seen a stock market this strong. These have been excellent times for investors. In the past 10 years, the S&P 500 index (SNPINDEX: ^GSPC) has delivered average annual returns of 15.3%. That means if you invested $10,000 in the Vanguard S&P 500 ETF (NYSEMKT: VOO) 10 years ago, today that investment would be worth about $41,523.

So why are so many investors feeling nervous? The S&P 500 recently reached a new record high on Oct. 6, with an intraday trading level of 7,844.52. As of this writing, the S&P 500 is down just slightly from that record high.

All-time highs in the stock market might sound like good news, but many investors see them as a bad sign of things to come. Will the stock market crash after all-time highs? The good times can't keep going forever, right?

Here's a surprising fact about the stock market: Just because the S&P 500 is hitting new record highs doesn't mean it's a bad time to invest. Stocks can keep growing. Good news can build upon itself. Bull markets can last longer than you think.

Let's look at why now could be a good time to buy stocks -- especially if you're a patient investor with a long-term perspective.

Image source: Getty Images.

S&P 500 record highs are often the best times to invest

Many investors instinctively feel like new record highs in the S&P 500 are a sure sign that the market is about to pull back. But history shows that's not true.

Fidelity researchers analyzed S&P 500 returns since 1920. They found that investing in the S&P 500 at all-time highs delivered higher returns than on all other days. The returns were even better for longer-term investors. In the past 106 years, since 1920, if you had invested on days when the S&P 500 reached an all-time high, your investment would deliver an average 63% return in the next five years -- versus only 58.8% in five years after investing on all other days.

The stock market tends to go up and keep going up. Since 1928, the S&P 500 has delivered average annual returns of 9.98%. New record highs don't have to be an ominous sign of bad news to come. Just the fact that the stock market keeps going up might be a positive sign that many investors want to buy stocks and that many people are seeing the potential for strong economic growth and rising corporate earnings. Good news in the stock market can compound like compound interest.

And even if there is a short-term sell-off that follows a new record high, the stock market tends to keep bouncing back even stronger in the long run. Companies figure out new ways to make money. Investors keep searching for the next exciting trend. The economy tends to keep growing through humanity's efforts to create, collaborate, and build the future.

The market's short-term performance will always be unpredictable, but the S&P 500's long-term potential is always promising. And new record highs are no reason to stop investing. Now could be a great time to invest in S&P 500 ETFs like VOO based on your risk tolerance and long-term time horizon.

Ben Gran has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.