The stock market has risen sharply since President Donald Trump's election win in November, but can those returns continue?
"These are hazardous times. These are not cheap times. In the market, one never knows what is coming next,"said Jack Bogle, founder of The Vanguard Group.
In an interview with CNBC's "On The Money," the retired chief executive of the index-fund giant sees a change in returns for individual investors in the stock market.
"The first thing they should do is plan for the future on the assumption that returns will be much lower than they have been in the past," Bogle advised.
He said since the long bull market began in 1982, investors have seen a nominal average return of 12 percent, minus a 4 percent inflation rate, for an 8 percent real return.
Today, Bogle says "we're looking for a 4 percent nominal return and one and a half to 2 percent inflation, for a 1.5 to percent real return on your savings. That's a big, big difference."
Despite the prediction of a lower return on the horizon, Bogle stressed: "There is never an argument for not investing."
"I've never been in favor of wholesale changes, like getting out of the market, or getting out of the bond market for that matter, but do something on the edges."