Go. Another very simple game that takes forever to master, and yet the rules can be tought in under a minute. It's also so complicated that the Go players of today are far better then the Go masters of 1000 or even 500 years ago because of all the strategy in the game that has been discovered and passed on. You can tell a lot about a person based on how they play Go... are they timid, aggressive, unwilling to make mistakes, willing to move without all the information? It comes out in a single game of Go.