From what I've read, generally speaking weightloss from dieting/exercise is usually 1.5-2 stones then you put back on .5 stone. Some people then revert back to original weight as they adopt their previous lifestyle.
It's got little to do with beliefs and delusions, far more to do with treating losing weight as a temporary thing then reverting to a previous lifestyle, thinking all I have to do is eat a little less, drink a little less than I did once I'm x stone. They end the diet with 'and now I shall be good because I'm happy' without actually intending to change their original lifestyle. They never intended to keep up the diet indefinitely. So they never had a belief that a diet was how they should live the rest of their life, but made no serious attempt to change their lifestyle.
That's my impression of it anyway, having done this once to myself and now pondering on how I'm back to my original weight.
On a related note, I've certainly read of people saying that you can build up periods of concentration (e.g. in this instance it was writing), start slow with a couple of hours and build up every day and eventually you can work yourself up to long periods of time of concentration without noticing it. This is perhaps a habit changing method.
I don't know, I'm no expert, that's just my best guess.