Definition
Cue is the signal — a time, place, person, emotion, or preceding event — that triggers a habit by predicting a reward.
It is the first stage of the habit loop. A cue is whatever your brain has learned to associate with a payoff: morning light, a phone notification, the sight of the couch, the feeling of boredom.
Why it matters
How it works
There are five common cue categories Clear identifies: time (waking up, 3pm), location (kitchen, gym, desk), preceding event (after pouring coffee), emotional state (stress, boredom), and other people (a friend texts, a colleague says "lunch?"). Most cues fall into one or more of these buckets.
For building habits, the goal is to make the cue obvious and consistent. Implementation intentions specify the time and place ("after I pour coffee, I will read for ten minutes"). Habit stacking uses an existing habit's completion as the cue for the next. Environment design — putting running shoes by the door, vegetables at eye level in the fridge — engineers visual cues into your physical space.
For breaking habits, the goal is the opposite: hide or eliminate the cue. The most reliable way to stop snacking on chips at night is not willpower; it is not buying chips. The phone in another room cannot ping you. A cue that does not fire cannot trigger the loop.