Thanks to the 2008 crisis, "there are risks that we know," the founder of The Vanguard Group added, "but there are risks that we don't know even exist. And that's the problem. Every crisis is different. Every bear market is different."

As legendary investor Jack Bogle told CNBC's "Power Lunch" on Wednesday, "There are always blind spots or, as I have said, the fog of the stock market: Nobody really knows what's going on."

This week marks the 10th anniversary of the collapse of Lehman Brothers and the start of the Great Recession. And some experts say that another financial crisis is inevitable.

Still, while "there are a lot of signs of exposure in the market," Bogle said, that's not stopping him from investing. "Nothing right now would cause me to get out of a long term investment program and certainly nothing would stop me from continuing to put away my $100 or $200 of $500 every month in my 401(k) or my IRA."

That's because buying and holding for the long term tends to be an effective investing strategy, no matter the economic climate. As Bogle told CNBC: "If you hold the stock market, you will grow with America."

Warren Buffett agrees. "No matter what the headlines say … American business is going to do fine over time," the Oracle of Omaha told Judy Woodruff of PBS NewsHour in 2017. "Occasionally we go off the tracks with bubbles … but it will never permanently derail us."

In fact, when he bought his first stock in 1942, the headlines didn't look good, he noted: "We were losing the war in the Pacific."

Markets go up and down every day but that doesn't necessarily mean there's significance to every move. As an investor, it helps to be patient and to accept a certain level of uncertainty. Since buying his first stock, decades have gone by and, in all those years, "I've never known what the market is going to do the next day," Buffett said. "That's not my game. My game is to decide whether I'm in the right economy, which America has definitely been ever since that time."

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