It's almost the end of the year!
"But I have exams, and I'm sooooooooooo done!"
This is how my students are feeling, and I'm sure that teachers are also feeling similar! At some point in time our brains just stop, and then we're puzzled over the most simple questions, like the guy in this video.
(Although, yes, I do know that this truly is a brain-bending concept when you first learn it. )