"I just need more discipline"

Here's the belief the cycle runs on. The diets ended because you didn't hold. Other people hold. You have a biscuit on Thursday and it's over, and what that shows is a lack of discipline, and next time you'll have more.

Look at the envelope. How did each one end? I'd expect a list that reads like a single story. A biscuit, a birthday, a bad day, a meal out, a weekend. Different rules, different lengths, the same shape of ending. If discipline were the variable, you'd expect variety. Some would have ended from weakness and some from bad luck and some would still be going. Instead they all ended the same way, at roughly the same point, and that's the signature of a design rather than a character.

There's a body of research on this that goes back fifty years. Peter Herman and Janet Polivy, in a paper from 1985 called "Dieting and binging", set out the case that dieting causes the overeating it's meant to prevent. The founding experiment was earlier, in 1975, by Herman and Deborah Mack. They gave people a preload, a milkshake or two, and then a taste test in which they could eat as much as they liked. People who weren't dieters ate less after the bigger preload, which is what you'd expect. People who scored high on what the researchers called restraint, the habit of dieting and watching what they eat, ate more after the bigger preload. Having already broken their rule, they went on. The word for what they were doing in the researchers' account is the one you'd use for Thursday afternoon. Might as well.

I'm reusing a study that an earlier book in this series also leans on, and I'll say why. It's the finding that this whole book rests on. Restrained eaters, meaning people who diet, respond to a break in the rules by eating more, not less. The rule doesn't just fail to stop the eating. It's the reason the eating goes past the biscuit. A person who wasn't dieting eats the biscuit and stops, because a biscuit is a biscuit. A person on a diet eats the biscuit and it becomes a write-off, because the biscuit broke something.

A bridge built for a load it can't carry is a fair comparison for two sentences. When it goes, nobody says the traffic lacked discipline.

So the discipline you'd need next time is the discipline to never once break a rule, for the rest of your life, in a world with biscuits in it. Nobody has that, and the diet was designed on the assumption that you would, and that's not a design you failed. It's one that fails.