(Vote Leave supporters wait for London Mayor Boris Johnson to address campaigners during a rally for the ‘Vote Leave’ campaign on April 15, 2016 in Manchester, England. Boris Johnson is taking part in a 48 hour ‘Brexit Blitz’ of campaigning in Northern England. Britain will vote either to leave or remain in the EU in a referendum on June 23.Christopher Furlong/Getty) Much of economic theory is built on the assumption that individuals are rational. They act out of self-interest, they run cost-benefit analyses, they don’t make mistakes. If they’re deciding whether or not they want something, they figure out what it will cost and how happy they’ll be if they have it, and they act — or vote — accordingly. Of course, people in the real world don’t quite work like that. The upcoming Brexit vote is a good example of individuals diverging from this kind of purely rational behavior, according to Richard Thaler, a behavioral economist at the University of Chicago Booth School of Business. The British citizens who are campaigning to leave the EU aren’t acting or thinking the way traditional economics would expect them to.