Perhaps you've heard that roughly three-quarters of all mutual funds lose to the market over the long run. The question is why -- why do presumably smart and talented managers serve you worse than simply buying an index fund? Believe me, I've met plenty of fund managers and the vast majority of these folks are talented and responsible and hard working -- they're not bad stock pickers.

The best explanation I've found comes from a recent study by professors Cohen, Polk, and Silli. Their study, "Best Ideas," provides pretty convincing evidence that the rules are stacked against smart fund managers. Their few very best ideas do perform well -- beating the market and their other picks by approximately 1% to 4% per quarter (which is significant). However, the very nature of a mutual fund requires managers to pick dozens -- perhaps hundreds -- of stocks.

Who can pick 100 good stocks? No one, really ... and having to load up a fund's portfolio with all these second-tier ideas seriously harms returns.

But what if ...
The knowledge that fund managers' best ideas tend to outperform might be profitable for us individual investors if we knew with certainty which stocks they most loved. One proxy for determining a fund's favorite ideas might be to look at its largest holdings. Take, for example, the giant American Funds Growth Fund of America, headed up by James Drasdo:

Growth Fund of America
Top 10 Holdings

% Net Assets

Microsoft (NASDAQ:MSFT)










Philip Morris International (NYSE:PM)


Bank of America




Coca-Cola (NYSE:KO)


JPMorgan Chase (NYSE:JPM)


Data from Morningstar; holdings as of June 30, 2009.

But is Microsoft really Drasdo's very best stock idea right now? We can't really know unless we bug his meeting rooms.

Maybe it is, or maybe Mr. Softy just grew to be Growth Fund of America's largest holding. Perhaps Drasdo has another great idea now that he's just starting to accumulate shares of -- and he's selling off Microsoft to do so.

There's lag time in reporting fund holdings, and who knows which company is on top now? You no doubt see the problem here -- we don't want to commit our hard-earned money to a guessing game.

So now you know the big reason for mutual fund mediocrity, and there's just no getting around it.

Unless ...
There's something of a silver lining in this study, however. If you're an experienced and competent investor, you can take comfort in the fact that you're not bound by the mutual fund rules. You don't have to buy dozens and dozens of companies; you can limit your investments to your very best ideas.

Our internal research at Motley Fool Stock Advisor backs up the conclusion of the "Best Ideas" study. Even better, however, is that you don't have to guess what its best ideas really are. Fool co-founders David and Tom Gardner have been offering up their five "Best Buys Now" each month since June 2006.

Our internal tracking shows these ideas, like the fund managers' best ideas, significantly outperformed the other stocks on our scorecard -- by a margin of 7 percentage points per pick. (The service as a whole is beating the S&P 500 by an average of 41 percentage points each.)

Interested in the five best ideas from Tom and David right now? For the next 30 days you can see them, along with all their recommendations, with a no-obligation free trial. Here's more information.

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This article was originally published on July 17, 2009. It has been updated.

Rex Moore drives on a parkway and parks on a driveway. He owns shares of Microsoft. Google is a Motley Fool Rule Breakers recommendation. Apple is a Stock Advisor pick. Coca-Cola and Microsoft are Inside Value selections. Coca-Cola is an Income Investor recommendation. Philip Morris International is a Global Gains choice. The Fool has a disclosure policy.