The Cue (Trigger)
A cue is the signal that prompts the behaviour. It can be a time, location, person, preceding action, or emotional state. Morning light triggers a wake-up routine. Walking past the fridge triggers a snacking urge. Your phone buzzing triggers checking messages.
Design strategy: Make cues visible and consistent. If you want to drink more water, put a glass on your desk. If you want to stretch, set a phone reminder at the same time daily.