21-day habit formation theory is myth 0
Countless self-help books and even marketing campaigns promoting oral healthcare have based their advice on the idea that it takes 21 days to form or change a habit. Though encouraging self-improvement and dental hygiene is generally positive and well meaning, the 21-day habit formation theory is actually a misinterpretation of information from the self-help book Psycho-Cybernetics by Maxwell Maltz.
Psycho-Cybernetics was first published in 1960 to introduce the idea of attaining goals by visualizing positive outcomes. Through his work as a cosmetic surgeon, Maltz found that it took an average of 21 days for amputees to adjust to the loss of a limb and extrapolated that changing one’s self-image would also take at least 21 days. Maltz was careful to point out that 21 days was an approximate minimum length of time to change a mental image and uses this example as a way to encourage readers not to abandon goals, but his idea became popularized as fact soon after publication — possibly due to an overwhelming lack of contradicting information.
In 2009, study results published by Phillippa Lally in European Journal of Social Psychology found that rather than taking 21 days, study participants took anywhere from 18 to 254 days to form a new habit with an average of 66 days. The new 66-day rule has become a popular counterclaim to the original 21-day rule, but even this study was limited to a sample size of less than 100 volunteer participants.
Many self-help authors have given merit to these claims and counterclaims presumably because there is little else to base their books on, just as many readers adopt these beliefs because it is the only information they’ve been presented with. However well intentioned, these books and beliefs may be, the fact still stands that habit formation is still a relatively mysterious process and consumers can be justifiably wary of companies that say otherwise to sell products.
What is known about habit formation is that people take different lengths of time to change or form new habits, but doing so is possible. Take as much time as you need.