Well of course it was - he was flesh and blood like the reat of us - but onstage he was manliness personified - the great hewer, the hunter for shoals of herring. You can't do that stuff for two hours a night without training. he was an actor for godsake - a great one!
That's why he could do Tam Linn - he had that focus, it was to him his King Lear - a longer soliloquy than Shakespeare would have dared to write..

has that really never occurred to you?

Did you ever see that Not the Nine o'Clock News Sketch - where they pretend to be interviewing Lawrence Olivier. Someone or other is there pretending to be Olivier sitting in very studied attitude with his unlit pipe as a prop.
One of the team asks, do you ever stop acting Sir Laurence?

that was Ewan! with his backward chair instead of a pipe! And credit where its due - he was a damn good act!

well he fooled you apparently.