I don’t know about you, but when I’ve heard people talk about this or have seen it in writing, it’s usually stated with a heartfelt level of conviction. I assumed that those in the know must be basing that number on something, some substantive evidence, despite the fact that the claims varied from 100 to 30 to 21 days.
Well, you can only imagine my surprise when a simple internet search proved this to be oh-so-unclear (um, this is sarcastic if you don’t know me yet). It turns out that the 21 day theory had its origins in a book by Dr. Maxwell Maltz published in 1960, called Psycho-Cybernetics. The validity of this theory is questionable, and a more recent study in the European Journal of Social Psychology reveals the magic number to actually be wildly varying, between 18 to 254 days, depending on the habit.
Other than getting frustrated with repeatedly trying to pronounce the word automaticity in it, there is some good reading about this in an article from Psyblog that you can access here. The good news from this research is that it seems to be fine if you miss a day while creating a new habit. The bad news is that it might take you 254 days to create a habit of doing 50 sit ups before breakfast.
Now this is just my take on this, but if a habit is that hard to create, it may be worthwhile to take a fresh look at the underlying goal and to readjust your activity to something that is simply more appealing to you, and therefore, easier to get yourself to do. In the sit-ups example, if your goal is to have strong abs, maybe a Pilates class, yoga, belly dancing or working out with a buddy would end up being a fun activity that would then be easy to stick with.
So, should you give up on the idea of sticking with something for a set number of days? Absolutely not! Try on your new habit for a few weeks and see how you feel. Are you resistant to it? Do you just hate doing it? Check in with yourself to find out why. Is there some other way to reach your goal? If you can’t think of another way, brainstorm with a friend for new ideas. You may be surprised to find that there are other ways to get what you want, and you may find some activity that you actually enjoy!