I’m a professor, which I suppose makes me a professional teacher. I instead like to think of myself as a professional learner. I believe that teaching is an extension of learning. It enhances learning. If I can teach you how to do something, it means I have learned it myself. There are other ways to prove this to myself; if someone is paying me to do something, there’s a pretty good chance I know how to do it. But if I can observe you doing it, as a consequence of my having taught it to you, that’s exponentially better proof that I’ve learned it.