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.