In stock investing, nothing stays the same forever. Yesterday's underperforming asset class could be tomorrow's overachiever.

This principle underlies asset allocation; by spreading your money around, you capture some of each asset class's upside, without exposing yourself to too much of its risk. Of course, these cycles don't have hard-and-fast timelines. But history gives us one clue: The worst-performing class over the last five years almost always moves up during the next five years.

So who's up next? There's a case to be made for large-cap stocks. Large caps have had a particularly rough ride since 2000 or so, underperforming much of the rest of the market -- until last year, when the category started to come back to life as fresh money flowed into big stocks.

Some of that flow had to do with rough conditions in the larger market, of course -- when times are turbulent, blue chips are more stable than small caps, generally speaking -- but that just illustrates the cyclical nature of asset-class leadership.

Large-cap performance has been held down somewhat in recent months, thanks to challenges facing big banks like Wachovia (NYSE:WB) and JPMorgan Chase (NYSE:JPM). If the broader market continues to drag, this shift could continue for a while.

And that would be great news for our retirement portfolios.

Everybody needs large-cap stocks
You do have a sizable portion of your retirement portfolio allocated to large-cap stocks, don't you? I think everyone needs some large-cap exposure in their retirement portfolios -- yes, even you, Mister or Miss Young and Aggressive Small-Cap Investor, would benefit from having 35% or so of your portfolio in large caps.

Why? Large caps -- especially of the blue-chip dividend-paying variety -- make a great foundation because they give you growth potential with less downside risk. Sure, large caps' low volatility limits their upward movement during bull markets -- but as long as you hold for the long term, reinvested dividends can go a long way toward compensating for that. And during down markets, the best of the blue chips hold their value much more effectively than smaller stocks.

Look at General Electric (NYSE:GE), a stock that's about as blue-chippy as blue chips get. Two years ago, back when the bulls still held sway, GE was trading at $32.80. And today, deep in a bear market? $29.00 as of yesterday's close -- and it has paid $2.30 in dividends over that period! Of course, it has shown some volatility during that stretch, but what it hasn't done is drop hard in the current market. Even great small caps like FormFactor (NASDAQ:FORM) and Ceragon Networks (NASDAQ:CRNT) can't say that.

Of course, not all large caps are blue chips, and not all "blue chips" are guaranteed trouble-free -- look at General Motors' (NYSE:GM) well-publicized challenges. Even Merrill Lynch (NYSE:MER) recently dumped $30 billion in troubled assets at a giant discount; it's now trying to raise money to offset the damage. I think Merrill has a good chance to recover, but meanwhile, its current price of around $29 is a long way from the almost $80 that those shares commanded a year ago.

That sort of uncertainty makes large-cap investing a little more complicated.

How to jump in
Given these big-name blowups, what's the best way for a retirement investor to grab a seat on the blue-chip express? Like us, Robert Brokamp, the lead advisor for the Fool's Rule Your Retirement newsletter, has seen the emerging case for large caps. In the new issue of Rule Your Retirement, available online at 4 p.m. ET today, he offers some excellent advice.

Check out the new issue for the nuts-and-bolts specifics -- yes, it's a paid service, but you can get a free 30-day pass with no obligation, so click with confidence. We kick things off with an article by Robert that makes the case for large caps in more detail, including a few surprising facts. (Trust me, it's even more compelling when he does it.)

After you've read the article, click on "Asset Focus" under the Resources tab. You'll see a list of investments carefully chosen by Rule Your Retirement analysts, together with complete instructions that take your age, goals, and overall portfolio into account. All you have to do is make the trades -- it's that simple.

You could pay an investment advisor several hundred dollars to come up with something similar -- or you could check out these recommendations and put them to work for you at no cost, with a 30-day trial of Rule Your Retirement. There's absolutely no obligation to subscribe.

Fool contributor John Rosevear owns shares of GM. FormFactor and Ceragon are Motley Fool Hidden Gems picks. JPMorgan Chase is a Motley Fool Income Investor recommendation. Try any of our Foolish newsletter services free for 30 days. The Fool's disclosure policy loves the blue chips, especially with chipotle-lime salsa.