NEW YORK (CNN/Money) - You're feeling trapped with an ailing portfolio, wondering for the millionth time if you should just get out of stocks for good.

The short answer? Don't.

"People tend to wait for the market to come back to get in, and typically they miss some powerful days," said Doug Flynn, a certified financial planner in New York. "It's the constant coming-late-to-the-party. It's technology after the fact. It's real estate after the fact. It's getting into bonds now."

Here are five reasons to hunker down and ride out the storm.

The Dow soared nearly 500 points Wednesday, a welcome change after weeks of punishing losses. And like most stock rallies, it came out of the blue. Anybody who rides out bad times in a money market fund misses out when the good trading days appear. Over time, investors who don't stay in the market pay for it with lower returns.

A study by Federated Investors in March found that you would have earned an annualized return of 15.1 percent if you kept your money invested in an S&P 500 portfolio between 1982 and 2001. But if you missed the 10 best trading days during that period, your return would have fallen to 12.2 percent. If you missed the 20 best days, you would have earned just 10.2 percent. And if you missed the 50 best days, your profit would have been just 5.4 percent.

Any stock market rally can fizzle (or not), and it's impossible to identify a turnaround when it happens. But investors who are in the market when the bulls return for good are the ones who are rewarded the most.

Indeed, you could see some of the strongest returns in the first year alone after a bear market ends. Research firm Thompson Financial looked at 15 bear markets since 1950 and found the S&P 500 earned 15 percent to more than 40 percent in the 12 months after the bear market ended. Following the 1973-74 bear market, for example, the S&P had a one-year cumulative return of about 38 percent.

Plenty of stocks and mutual funds are struggling so much that their five-year returns have turned negative. But there's no question that over time, stocks have outperformed bonds, money-markets and inflation.

Consider an analysis by Hartford Financial Services Group of two people who invested $100,000 at the end of the 1973-74 bear market. One kept all of the money in a CD. The other put half in a CD and half in the S&P 500.

By the end of 2001, the first investor saved $832,000. But the second investor who braved stocks had a nest egg of more than $3.1 million. That's two million good reasons to stick with equities.

All this might seem hollow with the S&P down nearly 35 percent since August 2000. But even in a worst-case scenario -- you bought at the height of the bull market and are now watching your money disappear before your eyes -- the pain won't last forever, according to figures from Ibbotson Associates.

In the Great Depression, S&P 500 stocks took 15 years to recover. But since then, the longest bear market drought has been four years. So if you had invested before the bear market in 1972, you would have lost 42.6 percent at the worst point and would have recovered your money by June 1976.

Other bear markets have been less punishing. If you invested right before Black Monday in 1987, your portfolio would have been down 29.5 percent at the worst point. You would have regained your losses in two years.

Sure, you may feel you can't take it anymore, watching your hard-earned dollars fly out the window. But Ibbotson doesn't see any reason to believe that this bear market is any different. It will end.

Still, you're obviously going to have to lower your expectations -- analysts are calling for returns of 7 to 10 percent in the years ahead. (Click here for more on what to expect with market returns.) There are plenty of statistics out there to scare you silly, such as the fact that it will take the Nasdaq until 2016 to recover.

But that doesn't mean you should avoid stocks. Rather, you should build a diversified portfolio so you can avoid the high risks of an all-stock lineup and make the best of a mediocre market.

Consider this example from T. Rowe Price. If you invested $10,000 in an all-stock portfolio between 1991 and 2001, you would have earned $33,736. But with a diversified portfolio of 60 percent stocks, 30 percent intermediate-term bonds, and 10 percent in Treasury bills, you'd have earned $27,223. If you had hidden all of the $10,000 in Treasurys you'd have netted around half that amount, roughly $16,000.

If anything, this market is a blessing in disguise for long-term investors. If you're in the market for 15 or 20 years, it's nice to know you can pick up Vanguard 500 Index for $77 after paying nearly twice that amount back in 1999. That makes dollar-cost averaging pretty appealing these days.

Dollar-cost averaging is where you commit to investing a fixed amount each month (say $50, $100 or whatever you can afford). If the share price plunges, your fixed dollar amount buys more shares -- as the share price increases, you're buying fewer shares. Over time, you've bought some shares in bull markets, when you're sleeping at night, and some in bear markets, when you're scared out of your wits. But your average cost is much lower than if you did all of your investing at the height of the 1990s bull market.