Too many irons in the fire?

Periodically I hear directors introduce themselves with "I'm a professional director". Sometimes, they add "I sit on XX Boards", where XX could be as high as eight or even ten Boards. Wow. Presumably this means all of their income comes from director fees, and somehow more Boards is better or more prestigious. Am I impressed? Not really.

The core role of any director is to maximise the performance of the company they serve. But how can they do this effectively if they spread their time across as many as eight or ten Boards? Ten Boards means a maximum of two days per company each month. In this scenario, how can any director possibly understand the issues and strategic options sufficiently well to contribute effectively around the Board table? 

Governing a company is demanding. It takes time to understand the issues. Can a director have too many irons in the fire? The stories starting to emerge in the media suggest the answer is a clear "yes".