The coldest thing is when someone refuses to teach, refuses to give the very possibility of learning.
We know we can’t give everyone every opportunity, but teaching is the opportunity that allows others to get more on their own. It’s the way we make up for what we can’t provide.
There is a pupil Socrates rejects – see the dialogue Theages for this account. But Theages has his choice of teachers and is recommended a specific direction for learning by Socrates. He also has the problem that he doesn’t want to do any good with any learning he gets.
Socrates in the Memorabilia only “rejects” one pupil, one who says that he has to visit her often as opposed to the other way around. That’s more in line with what I think of someone wise: A truly wise person can’t tell immediately when his pupils truly know or don’t know something. It takes a lot of familiarity, or the warranted assumption that a student can be trusted (i.e. “come see me often” isn’t what you want to hear a student say after meeting and teaching them initially), to see who understands and who doesn’t. The teaching process involves working with one’s students very closely, even while keeping a most necessary distance.
I wonder if I am acting justly in not trying to find more pupils, or being a bit “meh” about one or two that want to talk to me.