There is just so much to learn and I think many teachers--especially new teachers--are sometimes paralyzed by their sense of having to be the expert in everything. "I have to know everything because I must be this authority in my classroom." And what's most exciting as a teacher is to be able to say to your students, "Well, I'm not sure about that. But let's figure it out together." And to model for them an intellectual curiosity that ideally never ends in your life. I think that's why lots of us are in the classroom--because we want to have that learning forever and forever.