There are certain stock market lessons that most investors never learn. Among the biggest is "Beware of throwing money at a popular fund." That's one thing we should all take away from the career of Bill Miller, once the mutual fund industry's brightest star. Miller, who announced recently that he's stepping down next April, became a star money manager as his Legg Mason Capital Management Value Trust outperformed the Standard & Poor's 500 for an astounding 15 straight years. The longevity of that streak, which ran from 1991 through 2005, will probably never be matched. It was a fabulous performance.