Game design -- Similar benefits to chess. You're in a situation of perfect information and clearly-defined rules, and yet you still bump very quickly against the limits of your own cognition. You're forced to acknowledge and try to work around your limitations, because there are no excuses. Unlike in chess, there are no unsolvable problems; at worst, there are problems with no elegant solution.

It also illustrates the gap between what rules directly allow/prohibit, and what they actually incentivize doing. It requires that bit of economic thinking - what incentive systems are your rules setting up? What feedback systems does this result in?

Edit: Actually, it requires careful clear thinking about human biases in quite a few other things too! In order to even do what I wrote above, you have to avoid obvious biases in playtesting, if you want to figure out what a good player will do. But then you also have to account for the fact that most players will probably not be seriously focused on winning, and you will have to consider what their biases will lead them to do instead, so you can make sure the game is fun for them as well.