Earlier this spring I read, and very much enjoyed, Daniel Gilbert’s Stumbling on Happiness. Despite what the title might sound like, it’s not a self-help book. And, to tell you the truth, it’s not really about happiness. It’s actually about what makes us unhappy. In particular, it’s about why we are often so poor at predicting what will make us happy. The answer, it turns out, has a lot to do with our memories and, especially, the fragile, even malleable nature of our memories. I don’t know about you, but I tend to think of memory as something akin to a video camera, silently recording all of our experiences. It might be hard to...