Method acting is often depicted as an actor being "too in character" and "never breaking character". As if when you are playing Al Capone, you keep the accent up all the time, you bring your behavior in line with Al Capone's behavior, you even think like Al Capone, even off set. The depiction is that a method actor will become Al Capone, to the point of hardly needing a script.
That's an inaccurate depiction.
Method acting is using a set of practices (the "method" in the name) to draw upon your own experiences to bring yourself into an emotional state similar to the character's. It is, in fact, specifically about bringing notions and feelings from outside the fiction into the enactment of the fiction.
The problem isn't that the actor "is Al Capone". It is that, when they have a scene where they beat someone's head in with a baseball bat, the actor gets themself into the emotional state you'd need to be in for that action. Then, the director yells, "Cut!" and... those emotions are no longer appropriate, and cannot be processed normally while walking over the the craft services table for lunch.
This can make it very difficult to deal with the actor - "Cripes, Fred, why are you made at me? I'm just a props guy!" - and moreover it is not good for the actor's psychological health. Method acting is/was associated with emotional fatigue, and sleep loss/deprivation to the point of psychological disturbance.