Have you guys ever done something, whether it was work on an art piece or play a musical performance, that you thought wasn't going to receive well, but turned out to be terrific in the end? It's weird, the more I think my own artwork stinks (even though it looks decent on the outside) the more I find that people actually admire it later on.
I don't know, I suppose everyone has that "inner-critic" inside of them that keeps telling them that nobody will like the work. The fact that you are aware of your artistic abilities might also neglect the fact that you know more than your audience really cares to observe. Especially in music, if one played a couple of notes sharp in a five minute piece and the person freaks out, the audience won't know it.