All I can tell is that if you think you are funny, well-spoken, or smart, then you might not be. Doesn't this fall in the "duh" department? I'm surprised at the conclusion. Is it really lack of self-analysis, or is it just that people like to think of themselves in a positive light?
I know plenty of smart people who are not as funny as they think they are. Nothing wrong with that, I just don't think the phenomenon is limited to stupid people. It's human nature -- given the choice, I bet most people would rather be entertaining, than be entertained.