Left to its own devices, the human brain resorts to one of its most emblematic tricks, maybe one that helped make us human in the first place. It time-travels. ​ The whole sequence is a master class in temporal gymnastics. ​ The PET scanner allowed us to appreciate, for the first time, just how complex this kind of cognitive time travel actually is. ​ “Apparently, when the brain/mind thinks in a free and unencumbered fashion,” she wrote, “it uses its most human and complex parts.” ​ Amos Tversky once joked that where probability is concerned, humans have three default settings: “gonna happen,” “not gonna happen” and “maybe.” We are brilliant at floating imagined scenarios and evaluating how they might make us feel, were they to happen. But distinguishing between a 20 percent chance of something happening and a 40 percent chance doesn’t come naturally to us. ​ The Homo prospectus theory suggests that, if anything, we need to carve out time in our schedule — and perhaps even in our schools — to let minds drift.