From CNN:
By Kasandra Brabaw, Anastasia Buyalskaya, Angela Duckworth and Katy Milkman
As you’re drafting your New Year’s resolutions, you may think that it takes 21 days of repeating an action for that action to become a habit. So, you set out to go to the gym for 21 days, thinking that by day 22 heading to the gym will feel automatic — maybe even fun. It can be daunting to think about going to the gym for a whole year, but 21 days is doable.
We hate to burst your bubble, but that 21-day estimate isn’t true. According to habit expert and myth buster Wendy Wood, this falsehood came from a self-help book in the 1960s and actually described how long it takes to get used to your new appearance after plastic surgery.