The production as a whole is much larger than just one single actor. The director has a vision for the end result and will determine exactly how an actor fits into that. You will often receive notes and extra directions during the rehearsal process such as a new way to deliver a line or a new approach to playing a character. You need to be able to follow these directions to the letter and immediately take on board the new direction. A director will get frustrated if they keep having to repeat themselves.
