The default network quiets down when we perform a specific task, such as calculating a math problem in math class or studying ancient Greek pottery in history class. But when the mind’s chores are done, it returns to Old Faithful—the default mode. In other words, the brain’s free time is devoted to thinking socially. Consciously or not, it seems to be processing (and perhaps reprocessing) social information, as well as priming us for social life. It might be using this time to integrate new experiences into our long-standing knowledge of other people, their relationships with one another, or our relationships with them. It might be used to extract information from recent interactions to update the general rules we use for understanding the minds of others. This neural habit is at work in two-day-old infants and in our adult brains the moment we stop whatever else we are doing. In essence, our brains are built to practice thinking about the social world and our place in it.