Paul Schofield said something like, 'If I'm not acting in a play, I don't really exist.' Those weren't the exact words, but he meant it's only when I'm acting in a play that I've got something to say about the world. And then why should I talk, when people can come to see it?
Cinema gives you the opportunity to be both a grandparent and a grandchild whereas in life you cannot be both at the same time.