When a painting really lives, has a right to exist on its own strength and weaknesses, I consider it finished. When I have put all I can into it and it really breathes, I stop. There are times when a work has pulled ahead of me and goes on to become something new to me, something that I have never seen before; that is finishing in an exhilarating way.

Brice Marden
From the installation of his show at the San Francisco Museum of Modern Art