There are three parts to a habit loop: 1) Cue, 2) Routine, and 3) Reward.
1. The Cue indicates that there’s an opportunity to engage in a useful Routine that will end in Reward.
2. The Routine is the subject’s learned response to the Cue. It is typically an action or set of actions.
3. The Reward determines whether the Cue is worth remembering in the future.
For a habit to be created, it must have a distinct Cues and Rewards. The Cue is simply a signal that leads the subject to beneficial outcomes amidst the noise of day-to-day life. If the subject does not receive a Reward from executing the Routine, the reason to engage in the Routine disappears. And although the Routine will likely be remembered, the Cue will disappear back into the noise. Therefore, Habit Loops must have a Cue that the subject notices and a Reward that the subject rates as desirable (or at least a Reward that its basal ganglia or dorsal medial habenula finds desirable).
The Power of Habit by Charles Duhigg