Life is full of choices, sometimes too many choices. Should you buy the SUV or the gas-saving hybrid car? Should you have the artery-clogging cheeseburger or the lean turkey sandwich? Sometimes we make the "right" choices, but other times we make the choices of fools. Oddly enough, those foolish choices don’t usually bother us for long. Instead, they are quickly rationalized until the guilt goes away. Why are humans so good at fooling themselves? Recent research by Louisa Egan, Laurie Santos and Paul Bloom at Yale University demonstrated with capuchin monkeys and 4-year-old kids that the ability to self-deceive is deeply engrained in us primates. Capuchins will choose one color M&M over another (and let's face it, all M&M's taste the same) and then downgrade the other color, and little kids will do the same with stickers. Our brains, then, weren't so much designed to make choices as to pretend, no matter what, that we made the right choices. The goal seems to be mental peace; as we all know too well, the time from bad choice to righteousness is very uncomfortable and so the sooner we justify our decisions, the better. Thank goodness. Is there anything more irritating than a dinner partner who goes on and on about what they ordered? "Maybe I should have ordered the chicken, not the fish" heard over and over throughout dinner is enough to lob a fork across the table. How many times can you roll your eyes at the friend having an extramarital affair who keeps explaining away his bad behavior by saying, "But my wife and I have grown apart." We hate to hear endless backpedaling from others, and yet we do it every day ourselves. This kind of shilly-shallying is, in fact, so prevalent in human behavior that it must have some evolutionary basis. That is, it must be advantageous. Embarrassing and annoying, but advantageous. How? For one thing, the brain needs to get on to other, more important decisions. Worrying about something as silly as the choice of a new pair of shoes distracts a person from the truly important choices in life, such as how to find a mate and pass on genes. Also, the worried brain is a useless organ. When the time comes to make evolutionarily significant decisions, such as jumping out of the way of a car and making sure your genes aren't eliminated form the gene pool, it's a good idea to have a clear head. One doesn't want anxiety about the choice of paper vs. plastic to get in the way of feeding the baby, that packet of one's genes. Rationalization, then, is the background noise that clears the mental air. It's our way of patting ourselves on the back in congratulations and reassurance, saying to ourselves in a comforting voice, "Really, this choice is great, the best choice. You were right. Now, can we get on with it?" Meredith F. Small is an anthropologist at Cornell University. She is also the author of "Our Babies, Ourselves; How Biology and Culture Shape the Way We Parent" (link) and "The Culture of Our Discontent; Beyond the Medical Model of Mental Illness" (link).