If we can just keep it up for 21 days, it'll become a habit, right?
Not so fast. The three-week rule is something of an urban legend
, found a study led by Phillippa Lally, PhD, a psychologist at University College London. It actually took people 66 days
(9.5 weeks) for a behavior to become automatic (or feel weird not
to do it). But that's just an average. Some habits, such as drinking a bottle of water after lunch, turned out to be much stickier (it took 59 days on average) than doing 50 sit-ups each morning (91 days). Forging a new habit gets easier and easier as you gain momentum, Lally says. Eventually you'll stop counting the days...and just do it.