And that’s how society started spreading the common myth that it takes 21 days to form a new habit (or 30 days or some other magic number). It's remarkable how often these timelines are quoted as statistical facts. Dangerous lesson: enough people say something enough times, then everyone else starts to believe it.
It makes sense why the “21 Days” Myth would spread. It’s easy to understand. The time frame is short enough to be inspiring, but long enough to be believable. And who wouldn’t like the idea of changing your life in just three weeks?
How Long it Really Takes to Build a New Habit
Phillippa Lally is a health psychology researcher at University College London.
In a study published in the European Journal of Social Psychology, Lally and her research team decided to figure out just how long it actually takes to form a habit.
The study examined the habits of 96 people over a 12-week period. Each person chose one new habit for the 12 weeks and reported each day on whether or not they did the behavior and how automatic the behavior felt.
In 1960, Maltz published that quote and his other thoughts on behavior change in a book called Psycho-Cybernetics (audiobook). The book went on to become an blockbuster hit.