Morningstar Inc.(Stock Quote: MORN), the market-data firm, has released the finalists list for its Manager of the Decade award, to be announced early in the New Year.

So, what investing truths can be gleaned from the top-performing mutual fund mangers?

To be blunt about it: not very many.

Most investors would be thrilled to have held shares in any of these top-performing funds. The financial markets were hit by two terrible downturns during the decade, leaving the average stock fund nearly flat, though many bond funds did pretty well.

Morningstar says only a third of funds specializing in U.S. stocks managed gains for the decade. But the five finalists in the domestic-stock category each returned more than 10% a year.

The top performer, the Fairholme Fund (Stock Quote:FAIRX), managed by Bruce Berkowitz, returned 13.02% a year from Jan. 1, 2000 through Nov. 16, 2009. How did he do it?

Morningstar says: “Berkowitz focuses on free cash flows and has a deep knowledge of the businesses he owns and the management teams running them: a strategy pursued by many, but unrivaled by most.”

You could learn a bit more by poring through the fund’s prospectus and regular reports, and by evaluating its list of holdings. But it’s unlikely that doing all this would equip you to duplicate Berkowitz’ success. For one thing, the list of stocks in the fund is only a snapshot on the closing day of each semi-annual report. You’ll never know what stocks were bought and sold in between reporting deadlines.

Also, the fact that Berkowitz employs a “deep knowledge” of the firms he invests in doesn’t tell you which aspects of that knowledge are most important. Fund managers don’t reveal their secret formulas for obvious reasons: they don’t want competitors to know.

Free cash flow, a figure mentioned by Morningstar, basically means cash coming into a company minus expenses for capital improvements. Even if you understood the ins and outs of calculating this statistic, you would not know just how Berkowitz figures how much free cash flow is too little, too much or just right.

In other words, there’s no way to know exactly how the most successful fund managers do it.

Many investors are eager to conclude that, however they do it, the top managers can continually produce enviable results. Investors therefore pour money into funds with good track records.

But it’s impossible to know the extent to which a manager’s past performance was luck rather than skill, or whether he or she could thrive under different market conditions in the future. If thousands of fund managers flipped pennies, some would flip 10 heads in a row, but they’d be no likelier than anyone else to flip 10 more heads.

And even if the investor is dead certain the manager is a genius, the manager will someday retire, quit or get run over by a bus.

“We've narrowed the field to five nominees for each award: domestic, foreign, and fixed income,” Morningstar says. “We should point out, however, this is not a list of names for the next decade.”

All this uncertainty helps explain why so many investors have embraced index-style funds, which simply track market indicators rather than try to beat them.

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