The science
Writing it down: 138 randomised trials
Keeping a record of what you did changes what you do, and more so when it's physically recorded. Holding the ring is that record.
Harkin et al., 2016, Psychological Bulletin, 19,951 people
How long a habit takes: 18 to 254 days
How long a new habit took to feel automatic, person to person, among the people whose data fit a curve. There is no fixed number, so Forvel never promises one.
Lally et al., 2010, European Journal of Social Psychology, 39 of 96 people
What we leave out, and why
The number everyone quotes, 66 days, is the middle of the 39 people whose data fit a curve in the same study. Among those same 39, it took anywhere from 18 to 254 days. A fixed number would be a countdown to a date that isn’t yours, so Forvel keeps the week you planned, and the reps only go up.