As an elementary school student, a teacher once told me, very politely and apologetically, that I couldn’t have something reasonable that I wanted in class because that would mean that other students would be entitled to the same thing, which would be bad for the class. I’ve long since forgotten exactly what the situation was, but I remember the lesson–sometimes, things which might be justified must be denied because of the precedent that would be set.
In high school, a science teacher once scheduled an activity important to the class at the same time that another important activity was scheduled for a popular student club. Students couldn’t do both, yet both activities were good and valuable, and many students went into a tizzy, asking the teacher to change the day and time of his activity. He declined, explaining that the real world does not rearrange itself so that people can get to do every worthwhile thing they want to do–priorities must be set, and sacrifices must be made.
He was absolutely right. That was a crucial life lesson.