One of humanity’s biggest mental blocks is a reluctance to admit the functions of fun. Since we are intricately designed highly adapted and successful creatures, all of our major long-established behavior habits must have (had) important adaptive functions. And they must also be intricately designed, with many specific features that match the details of how such functions are best achieved. So, since we are inclined to spend a large fraction of our time on play and fun, such things simply must have important functions. Moreover, the details of our play habits must be intricately matched to the best ways to good ways to achieve those functions.