Acting is the discovery of--and journey into--oneself. There are as many cells in the body as there are stars in the universe.
Approaching a role, an actor must ask a series of questions: What do I and the character (at least as I interpret the character) have in common? Am I aware of that side of myself, the side that conforms to my character interpretation?
To play a killer, an incestuous father, or a saint requires that I understand the killer, incestuous father or saintly side of myself? Do I believe I have those sides of myself (emotional sides; because, remember, a performance requires that in order for the audience to feel, the actor must feel first)? And if I don't understand the character, is that because I don't understand that side of myself? And if I believe I have those emotional sides, do I have the courage and capability to feel and reveal those aspects of myself on demand, in front of people, excitingly and without interference generated by the requirement of speaking the instructed dialogue in the script and carrying out with exactitude the director's directed movements?
Actors often tire of playing a certain role. They get bored with the repetitive nature of doing the same character in a TV series for five years, for example. They want new; they want different. They want to explore a different aspect of themselves. They have in their career already chartered, mapped certain rivers of their emotional nature, and they want new discoveries. They are hungry explorers into the uncharted waters of themselves. They seek their own unknown; they want to experience new character (self) with full dimensions and digressions.
The hero seeks to play the heavy; the heavy seeks to play the lover; the man wants to explore his feminine, the woman want to swim flow freely in her stream of testosterone.
Who are we, the actor asks? What are unknown possibilities of our emotional life; or at least infrequently experienced selves? I want to hate beyond reason, to lust, to walk with death, to suffer the pangs of rejection and the joys of universal success. I want to be the courageous astronaut, the fearless fool daring to belittle the great King.
I want to act because the safety of the stage and the mask of the character permits me to be all that I can be.
The thrill, the seduction, the addiction of acting is wrapped up in just that: the infinite possibilities and challenges to actor's emotional courage.