You hold in your hands a compendium of information about self-delusion and the wonderful ways we all succumb to it. You think you know how the world works, but you really don’t. You move through life forming opinions and cobbling together a story about who you are and why you did the things you did leading up to reading this sentence, and taken as a whole it seems real. The truth is, there is a growing body of work coming out of psychology and cognitive science that says you have no clue why you act the way you do, choose the things you choose, or think the thoughts you think. Instead, you create narratives, little stories to explain away why you gave up on that diet, why you prefer Apple over Microsoft, why you clearly remember it was Beth who told you the story about the clown with the peg leg made of soup cans when it was really Adam, and it wasn’t a clown. Take a moment to look around the room in which you are reading this. Just for a second, see the effort that went into not only what you see, but the centuries of progress leading to the inventions surrounding you. Start with your shoes, and then move to the book in your hands, then look to the machines and devices grinding and beeping in every corner of your life—the toaster, the computer, the ambulance wailing down a street far away. Contemplate, before we get down to business, how amazing it is humans have solved so many problems, constructed so much in all the places where people linger. Buildings and cars, electricity and language—what a piece of work is man, right? What triumphs of rationality, you know? If you really take it all in, you can become enamored with a smug belief about how smart you and the rest of the human race have become. Yet you lock your keys in the car. You forget what it was you were about to say. You get fat. You go broke. Others do it too. From bank crises to sexual escapades, we can all be really stupid sometimes.