You can never get away from yourself

From Constantin Stanislavsky, An Actor Prepares:

Do you expect an actor to invent all sorts of new sensations, or even a new soul, for every part he plays? How many souls would he be obligated to house? On the other hand, can he tear out his own soul, and replace it by one he has rented, as being more suitable to a certain part? Where can he get one? You can borrow clothing, a watch, things of all sorts, but you cannot take feelings away from another person. My feelings are inalienably mine, and yours belong to you in the same way. You can understand a part, sympathize with the person portrayed, and put yourself in his place, so that you will act as he would. That will arouse feelings in the actor that are analogous to those required for the part. But those feelings will belong, not to the person created by the author of the play, but to the actor himself.

Never lose yourself on the stage. Always act in your own person, as an artist. You can never get away from yourself. The moment you lose yourself on the stage marks the departure from truly living your part and the beginning of exaggerated false acting. Therefore no matter how much you act, how many parts you take, you should never allow yourself any exception to the rule of using your own feelings. To break that rule is the equivalent of killing the person you are portraying, because you deprive him of a papitating, living, human soul, which is the real source of life for a part. (Trans. Elizabeth Reynolds Hapgood. Italics in original.)