Eventually, discipline research asks a question most don’t think to ask. Not if a habit is worth developing, and not how to develop a habit. This question is how long one can expect a deliberate effort to develop any given habit to take in order for the habit to develop enough to become almost automatic. The answer in popular culture is literature is almost always given with a vague, but a specific (and almost always the same), number of days. The number is a completely made-up number that has never resulted from habit formation research.
I. The 66-Day Study That Replaced a Myth
The “twenty-one-day” notion can be traced back to a 1960 book by plastic surgeon Maxwell Maltz, who noted that his patients took about three weeks to get used to a new face or missing limb and generalized that observation into a broader statement on how long any adjustment took. Over the years, this number was quoted in self-help literature without behavioral evidence to back it up so many times that it became one of those facts most people believe must have been proven by someone somewhere.
That, indeed, is worth a pause. What started as a measure of surgical patients’ psychological adjustment to a permanent change in their physical appearance has, over years of sloppy repetition, come to stand for how quickly an average daily behavior becomes automatic. The original observation never involved daily repetition or cue-based triggers, nor did it concern automaticity in the psychological sense in which contemporary researchers use the term. There is almost no connection between the two claims other than the three-week period and the general theme of change.