I think everyone in the theater wants to be a genius. I've never really met a theater artist who thought people were better than them at their particular field. I've met the best director in the world 20-30 times, the best playwright twice as often and the best actor? I meet him everyday. And even those of us who are humble, deep down have a belief that what we personally do is "true art" it's "real theater" and so in the rehearsal room we believe it should be respected. So, you often end up with a room of people who think they know more than the others around them and are saying "prove it to me, that you're so good" in every note session.
True. And we could take this as a template and lay it down over almost any other aspect of our lives. I can say this about business, academics, non-profit organizations even working out at the gym.