Researcher Wolfram Schultz wired up a monkey's brain and watched what happened when it received a drop of juice. The reward neurons fired. Gradually, Schultz added a signal before the juice arrived: a light that came on just before each drop. Over time, the neurons started firing when the light appeared, not when the juice arrived. The brain was anticipating the reward before it existed. This is craving. It is the neurological engine that drives every habit. Your brain does not just respond to rewards: it begins craving them as soon as it spots the cue. That craving fires automatically, before you have consciously decided anything. This is why habits feel so hard to break. By the time you are aware of the urge, the craving has already fired. The brain is already demanding its reward. Duhigg also explains why this matters for new habits. If you want to build one that sticks, you need to engineer a genuine craving for the reward. Gym chains play upbeat music, use nice equipment, and give members special towels because they need you to crave the feeling of going, not just decide to go.