Either a new realization or a reminder of an old one. All teachers, regardless of level at which they are teaching, ought to be well-versed in developmental psychology and should be continually be updating what they've learned about developmental psychology.
I strongly suspect that most teaching 'problems' (at least at the young adult level) are a consequence of teachers knowing nothing about where their students are developmentally (whether it's emotional, intellectual, whatever) and, perhaps more importantly, knowing nothing about our own intellectual and emotional development.
I think that we have a tendency to believe that any changes we've experienced since our time in college have (a) been non-existent and that who we are now is basically the same person we were then only with more experiences and knowledge but that our general way of seeing the world is basically the same - we have new knowledge, but not a new way of relating to that knowledge or, and this may just be a variant of (a), (b) been a result of simply more information, buckling down, really trying, etc. and can be duplicated by simply demanding that students believe the right things, buckle down, really try, etc.
With (a), we assume that our interests, questions, ways of looking at the world are the sorts of things that it's reasonable for our students to share insofar as there is really nothing all that different between them and us. We don't think of our current interests as being interests we have in virtue of where we are developmentally and, thus, not the sort of that students are going have. With (b), we just demand more out of the students and chastise them for not being in the same place, never recognizing that it's virtually impossible (at least that it's possible that it's virtually impossible) for them to do the things we are asking them to do, just like it's impossible for a 4 year old to really appreciate the importance of eating healthily.
When I think about my varying conceptions of 'friend' throughout my life, I realize that, given my current definition of 'friend' the folks I considered my best friends in junior high, high school and college wouldn't come close to meeting the standard. And I honestly think that at these younger ages I was literally incapable of seeing the world a different way.
Developmental psychology says that as folks go through adolescence, part of what happens is that they begin to realize that emotions are in them and not a trait of the thing causing the emotions. On another blog there's a discussion right now about teaching email etiquette to students (I'd say all etiquette) and it occurs to me that many of our students view their intended results as the only results that there are and that any other results are not their responsibility even if forseeable, predictable, etc. I suspect that young adults are so consumed with their inner lives and establishing themselves as an individual that they view the internal sense of themselves as that which is real and that everything else if not illusory is certainly insignificant and anyone who pays attention to clothes, language, hairstyle, etc. is just shallow. (Of course, I'm not saying that young adults live be these rules only that they hold others to them).
Anyway, I shall mull about this some more, but I think there's something to this (and, if there is, it's probably something already widely known and I'm just late to the party).