Why do three out of four professional football players go bankrupt? How can illiterate jungle dwellers pass a test that tricks Harvard philosophers? And why do billionaires work so hard - only to give their hard-earned money away? When it comes to making decisions, the classic view is that humans are eminently rational. But growing evidence suggests instead that our choices are often irrational, biased, and occasionally even moronic. Which view is right - or is there another possibility?