Everyone from Peter Lynch to your barber will tell you that before you invest in a company's stock, you should make sure it has great management. The best managers are agile enough to steer through trouble and exploit new opportunities. That's how Jack Welch at General Electric became a star and why GE perpetually trades at a higher multiple of earnings than the average stock. Welch is proven. You can buy his stock and throw it in a drawer. Ditto Charles Knight at Emerson Electric and Lawrence Bossidy at AlliedSignal.
But great managers today are switching companies more often. Buying a...