Ask people if they'd like a 15-cent Lindt truffle or a one-cent Hershey's Kiss, and 73% buy the truffle. Drop a penny off the price of each a 14¢ truffle or a free Hershey's Kiss and only 31% choose the Lindt. Is eating the chocolate you don't really want worth saving a penny? Probably not. But in the economics of life, we often show bad judgment, like allotting too much value to things that are free. In Predictably Irrational, behavioral economist Dan Ariely goes for a fascinating romp through the science of decision-making that unmasks the ways that emotions, social norms, expectations and context lead us astray. Mixing anecdote and social-science experiment, he illustrates common problems, like the tendency to keep our options open, even when one is demonstrably better. Consider the MIT student who has a horrible time committing to one of her two suitors despite her clear preference for one of them. And relativity gets us time and again: coffee in a nice setting tastes better; a person looks more attractive once a similar but less good-looking person enters the room. Understanding these irrationalities, Ariely writes, is the first step in overcoming them.