If you need stocks' high returns, you also get volatility

— -- Q: My retirement funds have been ravaged by the bear market, so I moved everything into bonds. But bonds do not generate ample returns for me to afford to retire. When will I know to move back into stocks?

A: You're making one of the most common errors made by investors. You're trying to time the market.

The stock market's returns can be huge. And over long periods, investing in stocks generally returns 10% a year, on average. But that tremendous return comes at a huge cost: risk.

You're not going to earn that 10% average annual return for free. You need to be willing to accept huge swings in the bargain. It's during these massive downdrafts that the solid returns are earned by investors who stick with their plan.

Trying to predict the market's direction is impossible, even for the pros. The disastrous returns of a vast majority of actively managed mutual funds illustrate that.

Why is it so hard? Timing the market correctly means being right not just once, but twice.

Not only do you have to get out before the market falls, but you have to know when to get back in. I've seen many investors get out in time to avoid the worst of a bear, but they got back in too late to enjoy the big, early rebound.

You're right. Bonds are less risky than stocks. Over the past 80 years, a global diversified basket of bonds has only deviated 3.67 percentage points from its annual average return, says IFA.com. That's stable. On the other hand, stocks have deviated a wild 19.2 percentage points from their average return. That kind of volatility is enough to drive investors out of the market, as we're seeing now.

But here's the key. Investors who hang onto stocks and endure the gut-wrenching jumps are rewarded over the long term. Over the past 80 years, a global diversified basket of bonds has only generated an average annual return of 4.93%, says IFA.com. That's a far cry from the 9.52% average annual return of U.S. stocks.

So here's the bottom line. If you can't handle the fact stocks are risky and will test your patience, you're going to have to stick with bonds and cash. But, that means you'll need to accept lower returns in exchange for greater stability.

If you need the higher returns offered by stocks, you need to stay invested and stick with your plan no matter what. Unless you have a crystal ball that will tell you the right time to get in and out of stocks, which I doubt, trying to time the market will not work.

Matt Krantz is a financial markets reporter at USA TODAY and author of Investing Online for Dummies. He answers a different reader question every weekday in his Ask Matt column at money.usatoday.com. To submit a question, e-mail Matt at mkrantz@usatoday.com. Click here to see previous Ask Matt columns.