Every year, [Tim Burton] spent an enormous amount of time on failed projects.
A few: Catwoman, Conversations With Vincent, Dinosaurs Attack!, The Fall of the House of Usher, Geek Love, Go Baby Go, Hawkline Monster, Lost in Oz, Mai the Psychic Girl, Mary Reilly, Superman Lives, X: The Man With X-Ray Eyes.
One key element of a successful artist: ship. Get it out the door. Make things happen.
Seth's Blog: Unrealized projects.
I love that Tim Burton is even willing to put this kind of info in his career retrospective instead of focusing on just his successes.