Richard Feynman wrote a letter to a former student, advising him to focus on problems that he can really solve or contribute to, rather than striving for grand or prestigious problems. Feynman emphasized the importance of finding pleasure and success in solving humble problems and helping others. He shared his own experiences of working on various problems, from simple to complex, and encouraged the student to evaluate himself fairly and find his own place in the world. The letter offers wisdom on how to approach problems and find fulfillment in one's work.