I've heard quite a few opinions recently on how to act in a film or play. There's often talk of "becoming a character" or "being someone else". I personally prefer the idea that characters come from within an actor. Is it possible that a human being has the capacity to pull from within himself thoughts, emotions, and experiences from which any character can be generated? A character is the sum of the lives of a writer, a director, and an actor.
Acting requires a high level of vulnerability and openness. It is showing the audience the pieces of yourself that you don't typically put on display; these pieces assemble a character. The deep self-presentation aspect of acting makes it common for actors to learn a great deal about themselves and their own personalities, even while playing roles they feel are vastly contrary to themselves.