Have you ever bought a new watch? When you first slip it on your wrist, you are keenly aware of its presence. The band rubs against your skin, and you find yourself glancing down, inspecting the clock more frequently than usual. Your thoughts habitually turn toward this new accessory and you might even show it off to your friends. After a couple of days, the novelty starts to wear off, and although you are still aware of the new watch, it doesn’t consume your thoughts. Weeks pass, and bef...