Popova quotes a passage from psychologist Jeremy Dean’s book Making Habits, Breaking Habits:
In a study carried out at University College London, 96 participants were asked to choose an everyday behavior that they wanted to turn into a habit. They all chose something they didn’t already do that could be repeated every day; many were health-related: people chose things like “eating a piece of fruit with lunch” and “running for 15 minutes after dinner.” Each of the 84 days of the study, they logged into a website and reported whether or not they’d carried out the behavior, as well as how automatic the behavior had felt. …
The simple answer is that, on average, across the participants who provided enough data, it took 66 days until a habit was formed. As you might imagine, there was considerable variation in how long habits took to form depending on what people tried to do. People who resolved to drink a glass of water after breakfast were up to maximum automaticity [acting without thinking] after about 20 days, while those trying to eat a piece of fruit with lunch took at least twice as long to turn it into a habit. The exercise habit proved most tricky with “50 sit-ups after morning coffee,” still not a habit after 84 days for one participant. “Walking for 10 minutes after breakfast,” though, was turned into a habit after 50 days for another participant.
The Dish 