[chris11]

This blog about the class seems to go a little more in depth:

"1. Carve out your areas of incompetence: There was some debate about the downside of such a principle (ie: young girls jumping quickly to say "I'm bad at math" when they might have a tremendous, although dormant, capacity for mathematics) but overall there are some apparent benefits to this practice. One tangible example was given of a consultant who joined some firm and, rather than follow suit with his colleagues and claim he could handle any of the potential tasks thrown his way, he chose to be very upfront, to carve out his areas of incompetence, and tell the people he worked with exactly what he wasn't good at. The story goes that he was promoted faster than any of his peers because of this practice."

http://thepowerofsocialtechnology.blogspot.com/

It sounds this practice helped his boss delegate tasks better and helped convince his that he was honest.