https://www.asc.ohio-state.edu/kilcup.1/262/feynman.html

Physics disgusts me a little bit now, but I used to enjoy doing physics.  Why did I enjoy it?  I used to play with it.  I used to do whatever I felt like doing – it didn’t have to do with whether it was important for the development of nuclear physics, but whether it was interesting and amusing for me to play with.

Richard Feynman