Kruskal's Paradox, also known as "The Riddle Wrapped in Enigma", is a mathematical puzzle that will drive you mad.
It's like a koan for the numerically inclined: "A man is a man, but a horse is a horse, unless it's a Kruskal, then it's a man."
Or, as the great philosopher once said, "I have a horse, but it's not a horse, it's a Kruskal. But wait, is it a horse? Ahh, the paradox is killing me!"
For those who enjoy existential crises and self-doubt, we recommend: