The Batman star was once one of Hollywood's top leading men, but Keaton lost his enthusiasm for cinema because he was repeatedly offered roles similar to parts he'd played before.
The actor admits he is his harshest critic, and constantly judging his past movies has kept him from taking on new projects.
He says, "I'm kind of not as interested (in acting) as I was in the past. Certain projects I thought I was either repeating myself or I didn't like what I did previously."
And he nearly turned down a part in film that would eventually become his directorial debut, The Merry Gentleman - until scriptwriter Ron Lazzeretti fell ill and Keaton was given the chance to take over.
He adds, "The writer was talking about directing it and frankly I wasn't sold on doing it that way, to be honest with you, and probably wouldn't have (starred in it). But then when he got sick and somebody said, 'You know they're going to go make that movie with another director,' I thought, 'I think I know how to make this movie.'"