There is a good editorial in the Journal of Chemical Education Cherry Picking: Why We Must Not Let Negativity Dominance Affect Our Interactions with Students
by Melanie M. Cooper
She emphasizes how it is easy to get discouraged by just a few students whose performance, preparation, actions, or attitude is disappointing to us. Furthermore, what is even worse is if that small minority ends up changing how and what we teach or what attitude we have to the majority of students.
I thought the following line was particularly important:
We must teach the students we have, not the students we want (or the students we imagine we were back in the mists of time).