It might be true that teachers do almost as much learning as the students in their charge.
My students teach me so much during our lessons, probably without even realizing it. It might be a raised eyebrow when we're discussing time signatures (a topic that brings up questions for most beginners--ugh, math!) and my challenge is to use new words, to figure out how their mind sees and understands, to use analogies and imagery and charts if necessary to help them make sense of it.
And as a pianist and piano teacher, there's an absolutely huge area of interest that I must constantly be educating myself on, because even if I spend a lifetime becoming familiar with it there will always be more--and that is the piano repertoire. The other day I decided that I was going to sight-read my way through all of the Haydn piano sonatas. Haydn has never been a favorite composer of mine and so I haven't played much of his music, but he's very important. I realized that the best way to alleviate some of my Haydn deficiency would be to get my own two hands on his music.
To be perfectly honest, even though I've been teaching for about ten years, occasionally I still feel like I'm floundering and have no idea what I'm doing. I've been blessed with such amazing teachers myself and they always seemed to be so naturally excellent at it. Sometimes I'll finish teaching a lesson and think: What did we just do? Did I explain that well? Should I be focusing more on theory? How do I get them to keep their wrists relaxed and their fingers firm? When should I introduce scales? How do I fix that terrible habit they have? This is so hard!!
But you know what? In my wiser moments I realize that this struggle is a necessary part of being a teacher, and becoming a better one little by little. There's no formula, no one right way. There's only trial, error, progress, failure, breakthrough, and always, utter commitment to the student and the music. And there's learning. I'll forever be learning.