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.

But of course, email and social media and games are obvious distractions. In my experience, the more subtle threat -- particularly for non-fiction writers -- comes via the eminently reasonable belief that you’re not ready to start writing, because you haven’t finished your research yet. ​ But as much as I enjoy it, I have learned the hard way that you are never done with your research. Waiting around for the research phase to be complete is a recipe for infinite postponement. ​ when you’re researching in media res, the new ideas or details or stories that you stumble across are much more useful to you, because you can immediately see the slots where they belong.