The myth of 21 days to build a habit

You've surely heard it: it takes 21 days to form a habit. The figure is as neat as it is false. It was born in 1960, when plastic surgeon Maxwell Maltz noticed his patients took 'about three weeks' to get used to their new face or to an amputation. That personal observation, nothing to do with brushing your teeth or going to the gym, became popular law.

The real science arrived in 2010. A team at University College London followed volunteers adopting a new habit and measured when it became automatic. The result? An average of 66 days, with cases ranging from 18 to 254.

In other words: it depends on the person and the habit, and it usually takes quite a bit longer than three weeks.

The good news is that missing a single day ruins nothing. Consistency matters more than perfection.