Feynman was not a theorist's theorist, but a physicist's physicist and a teacher's teacher. Feynman's theoretical concepts opened up research opportunities for experimenters, and his approach to physics dignified the role played by their work.
What is very important to me is two points: A theory should be internally consistent and it should have some contact with observation. Well, I’m told by all the experts that this theory [String theory] is internally consistent, although they think up new interpretations every time I turn my back. But contact with reality? Nobody’s given me anything. I just watch. I’m somewhat unhappy that so many people are working on it. To me, as a physicist, it’s sort of sad that so many people at the same time work at something that doesn’t seem to have any contact with experiment. But that, to some extent, is due to the fact that we don’t have any great experimental puzzle to be thinking about. We have to supply the puzzles, and there aren’t that many puzzles right now.
Telegdi, Valentine L. Interview by Sara Lippincott. Pasadena, California, March 4 and 9, 2002. Oral History Project, California Institute of Technology Archives. Retrieved January 11, 2010 from the World Wide Web: http://resolver.caltech.edu/CaltechOH:OH_Telegdi_V