I am forever seeing questions by youngsters asking, "what part shall I tryout for?" or "do I have a chance for the lead?" Then others are asking, "how do I become a famous actor?" And even experienced actors are saying what role they want in the next audition they are attending. Finally, I get questions from actors in plays in which they want to know how to deal with personality clashes amongst the cast or how to deal with some cast member who is difficult or who is incompetent.
All of these questions are egocentric and should not be the concern of the person asking them. If a person is going to audition for a play, he or she should do so with the intent of helping the show be a success. It is the director's job to determine how that can be done. If you will be most helpful as the lead, swell. If you can do that by being in the chorus, great! be the best chorus member ever and make the show terrific. If all you are concerned about is being famous, you have no business trying to be an actor. Fame is not such a good deal anyway -- with papparazzi following you everywhere sticking cameras in your face, with people writing fake stories about your supposed abnormalities of taste and behavior, and generally your not haveing any sort of private life at all, having to hire body guards, etc. Can't be any fun.
I write in my book, The Tao of Acting, about actors being the worst judge of what roles they can play. Take it to heart. It is only an ego thing to think you can be great as any role. The proof is in the doing, not in the thinking. It is the director's job to cast the show,not yours. It is also the director's job to prevent conflicts amongst cast members, to make sure that someone is not undermining the play with gossip and back biting, and to make sure that every actor in the show can give an effective performance. These things may worry you as an actor, and if they are not resolved by the director before the performance of the show, you might want to reconsider before working with the offending actor or the director again.
It all boils down to ego. We want to look good when we are in a show. We want to be seen as worthy and competent. We always will run into difficult situations and difficult people as we continue to work in the theatre and cinema. It comes with the territory. The best thing you can do is not be a difficult person and do your job well.