Mouni Sadhu (kind of a new-age crackpot, but a very to-the-point and convincing writer) wrote about this in his book Samadhi, which I think was published in the

Mouni Sadhu (kind of a new-age crackpot, but a very to-the-point and convincing writer) wrote about this in his book Samadhi, which I think was published in the 50s. He talked about starting off restricting small aspects of your behavior (like eating dessert), keep at it for 8 weeks or so at which point it becomes habitual, and then move onto tougher restrictions. But, if you start to ease back into the things you've already conquered, believing that "oh i'm strong enough to do this in moderation now", your tower of willpower will collapse. I don't know his methodology for getting this info, but it probably wasn't rigorous.