Quoted in a piece in the Sunday New York Times, Bruce Greenwald (author of the terrific Value Investing: From Graham to Buffett and Beyond) sums up Eddie Lampert's problems at Sears Holdings (NYSE: SHLD) beautifully: "He did really well on Autozone. Most of his stocks are retail stocks, and he has done really well with them. So he decided he was a genius at retail, and it didn't occur to him he could be wrong about it. He believed his own press."

I would argue that the problem might even run deeper than that: Lampert wanted to be seen, and to see himself, as more than just a great investor. He wanted to become a great manager.

It's somewhat similar to former all-star slugger Jose Canseco, who decided he wanted to try pitching. He promptly injured his arm and missed the rest of the season. His attempt at pitching hurt him as a hitter.

Lampert's fall from grace has been steep and rapid. We used to talk about how shares of Sears were trading at a "Lampert premium," based on the idea that his investment prowess would lead to great returns on capital for the struggling retailer.

Now, with Herb Greenberg recently having named him the worst CEO of 2007, shares of Sears are trading at a Lampert discount and are, according to many, currently valued at well below the company's break-up value. There may be value to be had in Sears, but Lampert's struggles provide an important lesson for investors: great investors aren't necessarily great managers, but, like Carl Icahn did with TWA, they might not be able to help themselves from giving it a try.