Teachers are rarely thought of as "just another human being" with their own thoughts, feelings, and experiences. Teachers are sort of glorified into grading machines. But when life appoints us as teachers, you suddenly realize that teachers don't know everything either. But it's precisely that--knowing that you don't know everything--that drives you to learn more, so that you can teach more. You want your students to know more than you ever did. You want your students to learn concepts earlier and faster than you did. You want to go farther than you. You want them to learn more than you ever will.
You want to keep the world evolving.