"If you have a 10-year time horizon" — meaning you don't need to cash out before then — "you have an 88% likelihood that the stock market is higher when those 10 years are up. That's starting in any month of any year going back to 1926," Brown says. "If you have a 20-year time horizon, it's 100%. There are zero 20-year periods where the stock market is down from the month and year you started."

Source: Los Angeles Times February 14, 2018 16:18 UTC