The NYT has a rather interesting article about.

"Sometimes repeat entrepreneurs have to be shoved out before they learn that their talents apply to start-ups, not to running bigger companies. That is why some venture capital firms include in their term sheets the stipulation that if the board deems it necessary, the chief executive must start a process to find a successor.

At other times, the company simply fails. But, for the serial entrepreneur, that is generally an incentive to try something else."