From Dr. Maxwell Maltz's book "Psycho-Cybernetics"
"Dr Maxwell Maltz wrote the bestseller Psycho-Cybernetics.
Originally a Plastic Surgeon, Maltz noticed that it took
21 days for amputees to cease feeling phantom sensations
in the amputated limb. From further observations he found
it took 21 days to create a new habit. Since then the '21
Day Habit Theory' has become an accepted part of self-help
programs.
Brain circuits take engrams (memory traces), and produce
neuroconnections and neuropathways only if they are
bombarded for 21 days in a row. This means that our brain
does not accept ‘new’ data for a change of habit unless
it is repeated each day for 21 days (without missing a day)."
http://www.aristotle.co.nz/library/s...px?seriesId=61
He also noticed that many of his customers retained a poor
self image even after having surgery which improved their
appearance. This prompted him to work with his clients'
self image prior to surgery, and he discovered that he could
assist them to acquire an improved self image without surgery,
using the same 21-day period to create changes in their
mindset, and that surgery then became unnecessary for them.