...when you're over your head with things you need to do, and you take a 2-day productivity marathon to try to get things done, and you do.
And so you end up with this free time and you don't know what to do with it.
I think this calls for some Ben and Jerry's and a movie.
Also, explaining logic to students is frustrating in two very different ways. 1) I don't understand how 205 students don't understand proofs. There are some premises, you alter those premises with some rules, and you get to a conclusion. Not difficult. 2) I never learned this 305 stuff when I took it. We never proved x=x; we were given an equality introduction rule that let us assume x=x. What's up with that.
But relearning things like Cantor's Theorem always excites me. Something greater than the infinite set of natural numbers? The universe is broken!!