The stock market
There are three rules to the game. One, you have to write your predictions down (otherwise, you’ll cheat, you devil). Two, you also have to write down the reasons for your predictions. Three, when you lose, you have to force yourself to analyze why you lost, why your reasons didn’t hold up.
If your ego needs an occasional cold shower, this little exercise will provide you with a lifetime supply. It will also force you to reexamine and adjust your reasoning without having to pay any penalty for being wrong. You’ll find that the more you do this, the more accurate you’ll become. And if you find you have a real talent for it, then, but not until then, you should back that talent with cash.