Psychologists define a habit as a behaviour that is repeated so often that it…

Psychologists define a habit as a behaviour that is repeated so often that it becomes automatic. Brushing your teeth, checking your phone when you wake up and taking the same route to work are all examples. Once a habit is formed, we perform it with very little conscious thought, which frees our minds to deal with other matters.

Researchers often describe habits as a loop made up of three parts. The first is a cue, a trigger that tells the brain to start the behaviour; it might be a time of day, a place, a feeling or the presence of certain people. The second is the routine, the behaviour itself. The third is the reward, a pleasant result that tells the brain the behaviour is worth remembering. Over time, the brain begins to expect the reward as soon as it notices the cue, and this expectation creates the craving that drives the habit.

This model helps to explain why bad habits are so hard to break. A person who eats a snack every afternoon may not actually be hungry. The cue may be boredom at work, and the real reward may be a short break and a chance to chat with colleagues. Simply deciding to stop eating snacks rarely works, because the cue and the need for a reward remain. A more effective strategy, many psychologists argue, is to keep the same cue and reward but change the routine, for instance, by taking a short walk with a colleague instead.

How long does it take to form a new habit? A popular belief holds that it takes 21 days. However, a well-known study carried out at University College London in 2009 suggested a more complicated picture. Participants chose a new healthy behaviour, such as drinking a glass of water after breakfast, and reported every day whether they had done it. On average, it took 66 days for the behaviour to become automatic, but the time varied enormously, from 18 days for some people to more than 250 days for others. Simple behaviours became automatic faster than complex ones.

Interestingly, missing a single day did not seriously affect the process. This finding is encouraging, because many people give up a new habit completely after one failure, believing that all their effort has been wasted.

Understanding the dynamics of habits does not make change easy, but it does make it more manageable. By identifying cues, choosing satisfying rewards and allowing enough time, people can gradually replace behaviours they want to lose with ones they want to keep.