" People in general, and knowledge workers in particular, grow according to the demands they make on themselves. They grow according to what they consider to be achievement and attainment. If they demand little of themselves, they will remain stunted. If they demand a good deal of themselves, they will grow to giant stature—without any more effort than is expended by the nonachievers. "

― Peter F. Drucker , The Effective Executive: The Definitive Guide to Getting the Right Things Done