Why do we do what we do? Is it inner drive? Is it compulsion due to financial need? Is it just because we like it? Certainly, all of these things can be a part of it. Maybe it's "all we know".....
I don't pretend to have answers about such lofty things, but it's something I do think about. I have been fortunate enough to have wonderful teachers my entire life. (and still do) It was due to that realization--that people have taught me really good things--that I decided to become a teacher. I wanted to try and give to another generation what was given to me. Maybe I've been ok at that--maybe for some, not as much. It's often difficult to tell. Do students do what you require of them due to them wanting to improve, and trusting you to guide them correctly, or do they merely do it "for the grade"? I like to think it's for the former, but at times, I know, it's due to the latter.
Motivation. It's an interesting thing.