Vanguard founder and former CEO Jack Bogle says investors shouldn't try to trade in and out of the stock market.

The investor noted many people sold their stocks when markets took a severe fall during the financial crisis, and these people missed out on all or part of the market's dramatic rebound since then.

"It shows you when you act on the emotions of the marketplace you're making a big mistake," he said Wednesday on CNBC's "Power Lunch." "Stay the course, don't let these changes in the market, even the big one [like the financial crisis] … change your mind and never, never, never be in or out of the market. Always be in at a certain level."

Bogle, 89, said he keeps 50 percent of his investments in stocks. He said over the long term there is a high correlation between the stock market and U.S. economic growth.

"Never be out and think you can get back in because your emotions will defeat you totally," he said. "Short-term betting is not a good way to go."

Bogle founded Vanguard Group in 1975. The firm is widely regarded as the leader of passive index investing. It has approximately $5.1 trillion in assets under management, according to its website.