Richard Feynman. Surely you're joking, Mr. Feynman! (№ 299511)

I don't think I could live without teaching. The reason is that I just need something to do and when I have run out of ideas or I don't get any results, I, as a teacher, all I can say to myself: "At least, I marvel a normal life; at least, do something, make some contribution" - a purely psychological reason.