Y combinator seems to be something mysterious. Several people have been trying to understand the intuition why it works. I have seen "A Lecture on the Why of Y" by Matthias Felleisen before, and while it does give me some insight, I still feel confused in some degree. That doesn’t prevent me from recommending this lecture to other people I talked to because it’s the best one I have seen so far.

Recently I thought about the fixed point combinator again and finally gained some good insight. I think it’s worth sharing here.