(The Nash Equilibrium) showed that in any competitive situation-- war, chess, even picking up a date at a bar-- if the participants are rational, and they know that their opponents are rational, there can be only one optimal strategy. That theory won Nash a Nobel Prize in economics. The math behind it is flawless and has transformed the way people think about evolution, arms races, stock markets, and ticktacktoe. There's only one problem: People aren't rational.