That’s the reason most theater people have always bothered me, they’ve successfully emptied themselves of self so many times that there’s no longer any “there” there. It’s all a performance and truth becomes a very malleable thing, to them. Some do become possessed, imho. An empty vessel will be filled.
I am reminded of a very telling moment in the film “The Saint” which features a tour de force performance by Val Kilmer adopting guise after guise in a totaly convincing manner.
At one point in the middle of te film he is confronted by the female lead who questions him “Who are you really?”
It is at this point I believe that Kilmer slips out of character and speaks as himself when he says “No one knows - least of all me.”