It is also work, and struggling to understand can be frustrating. But the exertion leads beyond. The subject might be math or astronomy, history or English, chemistry or German, politics or drama, chess or crossword puzzles, computers or cars. What they share is the challenge they pose, and the excitement that comes with mastery. The joy of teaching, as Harold Reiter puts it, comes in watching students succeed.
Some people succeed at a very high level.
Some, sadly, don't succeed at all, making teaching difficult and frustrating. Most of us are in the middle. We won't all find math fun, or breeze through all the problems offered at the math newsletter website, or excel in other fields. But it is not necessary to be a Michael Jordan to enjoy participating in sports, as millions of weekend athletes demonstrate. The world of the mind is just as invigorating.