When I was 13 I used to play D&D and sometimes we would bet with our gold. I came up with a betting system where I would bet on near 50/50 odds games like a coin toss against another player, and each time I lost, I would double my bet. I played around with the math and I figured out that I could get my odds of winning this way up to 99.99% before too long. But it took a few empirical tests to figure out why this wasn't such a great system...