One thing about Feynman is that he went to some trouble to arrange his life so that he wasn’t particularly busy–and so he could just work on what he felt like. Usually he had a good supply of problems. Though sometimes his long-time assistant would say: “You should go and talk to him. Or he’s going to start working on trying to decode Mayan hieroglyphs again.”

http://www.stephenwolfram.com/publications/talks/feynman/