https://www.wired.com/story/mathematician-terence-tao-cracks-a-dangerous-problem/

Experienced mathematicians warn up-and-comers to stay away from the Collatz conjecture. It’s a siren song, they say: Fall under its trance and you may never do meaningful work again.

The Collatz conjecture is quite possibly the simplest unsolved problem in mathematics—which is exactly what makes it so treacherously alluring.