Fun fact about Marathon Man:
There was an urban legend that, in preparation to shoot a scene where his character stays up all night, Dustin Hoffman (a determined method actor) actually stayed up all night for real, to which Sir Laurence supposedly replied "Oh, Dusty, why don't you try ACTING? It's much easier."
The real reason Dustin stayed up all night was because he was going through a divorce and was very depressed so he stayed out partying all night. Sir Laurence suggested acting as a way to beat the stress of it.