Funny Picture

Robert Redford apparently now thinks he wrote All the President's Men.

Quite a few actors seem to have a habit of convincing themselves that they wrote or improvised stuff they didn't. I wonder why?

Is it because in order to act, they have to convince themselves that they're not a character saying lines, they're a real person saying all that stuff in a real situation? Therefore how could someone have written anything?

Or is it because movie stars just have big heads? (This is an objective fact. Robert Redford has a gigantic head.)