There is a story, probably apocryphal, about Sir Laurence Olivier and Dustin Hoffman on the set of Marathon Man. There is a scene where Hoffman's character has been awake for a few days and is physically exhausted. So on the day they were to film that scene, Hoffman came to the set in terrible shape, and Olivier said, 'Dusty, you look absolutely wretched!'. According to the story, it turned out that Hoffman had been awake for twenty-four hours and had been running laps around a track, in order to prepare for the scene by making himself sleep-deprived and exhausted. On learning this, Olivier shakes his head and says, 'Oh, Dusty, why don't you just try acting?'
My first introduction to the world behind the stage came from reading Robert Heinlein's Double Star when I was a teenager. I get flashbacks to Double Star from the Olivier story, and from the following video clip where another great actor, Sir Ian McKellen explains his acting method.