A habit is a behavior that has been repeated enough times to become automatic. Once a habit is firmly established, it is performed with little conscious thought, because the brain creates neural pathways that conserve energy and cognitive resources. The defining feature of a fully formed habit is its automaticity, the degree to which a behavior happens without conscious thought. Automaticity increases gradually with consistent repetition until it reaches a plateau.
Habits operate through a structure Charles Duhigg called the habit loop, which consists of three components: a cue, the trigger that initiates the behavior; a routine, the actual behavior; and a reward, the positive outcome that reinforces the loop. The cue can be a time of day, a location, an emotional state, other people, or a preceding action. The routine is the behavior itself, whether physical, mental, or emotional. The reward satisfies a craving and tells the brain that the loop is worth remembering for the future.
Context plays a major role in habits. The time, location, and preceding events associated with a behavior become strongly linked to it through repetition, which is why exercising at the gym feels more automatic than exercising at home. When you travel or experience a major life change, those environmental cues often disappear, breaking the automatic trigger. A single habit is one behavior performed automatically in response to a cue, while a routine is a sequence of behaviors performed regularly; a morning routine, for instance, may consist of several individual habits chained together.