From a speech by William Graves, editor of National Geographic magazine, Speaker's Idea File
Years ago, after a celebrated international career on the stage, the world-famous violinist Jascha Heifetz became a professor of music at UCLA. When someone asked him why he had left the glamour of performing to become a teacher, Heifetz answered, "Violin-playing is a perishable art. It must be passed on; otherwise it is lost." Then he went on to say, "I remember my old violin professor in Russia. He said that (if I worked hard enough) someday I would be good enough to teach."