What goes wrong when you ignore that the reward must satisfy a craving?

The most common reason fails: Confusing the surface reward with the underlying craving. You assume your afternoon snacking habit is about hunger, so you replace chips with carrots — but the craving was actually stress relief, and carrots do not relieve stress. The replacement fails within days because it satisfies a need you did not actually have while ignoring the need you do. A second failure mode is never testing: accepting your first hypothesis about the craving without running experiments to verify it, then building an entire reward structure on an incorrect foundation.

The fix: Select a habit you are currently building or attempting to build. Write down the reward you have been using (or assuming). Now run Duhigg's craving isolation protocol: the next three times the cue fires, try a different reward each time. After each alternative reward, wait fifteen minutes and write down whether the craving is gone or still present. If the craving persists, that reward missed the real craving. If it dissipates, you have found the underlying need. Document what you discover about the gap between the reward you assumed and the craving you actually have.

The underlying principle is straightforward: The reward works because it satisfies an underlying craving — identify the craving.