In order to protect my image of being smart, I would avoid situations where I could make mistakes or appear less intelligent than I thought I was. And so I wouldn't try new things, and I would stay away from any activities that could "out" me as not actually being smart. Its really a vicious cycle, and the result was that I was far less productive & useful than I should have been.
Now I try to project an image of being hard-working instead. It frees me from having to constantly worry about messing up -- all that matters is that I get the job done. And I think I'm much better for it.