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I've been working for five years now and save religiously for retirement. But I feel that I've begun investing at a bad time for the markets. Most of all I worry about what will happen to my 401(k) if the market tanks again. Am I right to be concerned? -- Aaron, Nashville, Tenn.

It would be nice if I could assure you that the market gyrations that have spooked investors recently and over the past dozen years -- i.e., stock prices dropping by 50% or more in 2000 and 2007 -- aren't likely to occur again. But I can't do that.

If anything, recent research shows that these sorts of gut-wrenching episodes -- while not exactly the norm -- are likely to occur more frequently than we previously believed. So I can virtually assure you that over the course of your career, the market will tank many times.

But I don't think that's something you should worry about when you're investing for retirement. Investors have gone through many tough times before.

Since 1929, we've had 14 recessions and 13 bear markets, an average of about one of each every six or so years. And each time stock prices eventually recovered from these setbacks and climbed to new highs. I see no reason for that dynamic to change.

Besides, as counterintuitive as it may seem, you may actually be better off starting to invest in a lousy market if you're just beginning to save for a retirement that's many years down the road.

Related: What is an index fund?

A T. Rowe Price study from a few years ago examined how four hypothetical retirement investors who put their savings into a diversified portfolio of stocks would have fared over four different 30-year periods depending on whether they began investing on the eve of a bull market or a bear market.

I'll spare you the details, but the upshot is that the investors who got their start in a bear market accumulated more than twice as much in savings as those who began investing on the verge of a bull. The reason: the shares that investors acquired at depressed prices during a setback soared in value as the market rebounded, significantly boosting the eventual size of their nest egg.

Of course, neither you nor I really know whether this is, as you fear, "a bad time for the markets." Bear and bull markets are easy to identify in hindsight, but difficult to impossible to predict in advance. If that weren't the case, everyone would get out of the market just before it drops precipitously and jump back in just as prices are rebounding.

So it makes little sense to try to time your retirement saving and investing based on what you think the market may or may not do. The most you can do is play the cards you're dealt as best you can.

As a practical matter, that means investing most of your retirement savings -- say, 70% to 90% -- in stocks at the beginning of your career when you have plenty of time to recover from those inevitable market downturns. As you get older, you can begin shifting more of your savings to bonds.

You can expand beyond a simple stocks-bonds portfolio if you like. But don't feel you have to load up on all the gimmicky little niche investments Wall Street's marketing machine churns out. In general, a simpler mix is better.

Related: What is the right mix of stocks and bonds for me?

By the time you're ready to retire -- and more interested in protecting your nest egg than growing it -- you probably want to have roughly 50% of your savings in stocks and 50% in bonds. For a guide of how to achieve this transition, you can check out the "glide path" of a target-date retirement fund. After you've retired, you can then shift your focus on the best way to turn your savings into retirement income.

But however worrisome you may feel the outlook for the economy and the markets may seem today, what with the constant talk of the fiscal cliff at home and the debt crisis abroad, you would be making a big mistake if you let your anxiety sidetrack you from continuing to save diligently for retirement and putting 401(k) money into the investment that's generated the highest long-term returns in the past and is likely to do so in the future -- stocks.