Most executives wouldn't consider themselves "fortunate" if they took over one of the largest fund companies weeks before an historic market collapse. But then, most executives aren't taking over Vanguard Group at a time when investors are moving assets to low-cost index funds.

"It has been a tumultuous period, but Vanguard is coming out of this ahead," said F. William McNabb III, who became the company's president and chief executive in August. "It illustrates the power of diversification, and that is a very important point. I know it must sound like motherhood and apple pie, and it sounds pretty basic, but competitors lost sight of it. They lost sight of it in the late 1990s and they lost sight of it recently. Our success comes down to remaining disciplined."

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