"I've tried the small bags and I just open two"

Here's the objection from a reader who's already tried chapter 21's method. Small bags. Multipack. And on the sofa, the first one went and the hand went back to the multipack and opened a second, and sometimes a third. The partition didn't partition.

Two things. The first is arithmetic. Two small bags is sixty grams. The sharing bag was a hundred and fifty. A person who opens two small bags has eaten forty per cent of what the run would have taken, and if that's failure, it's a failure that leaves ninety grams of crisps in the cupboard every night. Three small bags is ninety. The multipack was doing its job on the nights you thought it wasn't, and the job wasn't perfection. It was less.

The second is what happened between the bags. You finished the first one. There was a moment. In that moment you decided to open another, and then you did. Cheema and Soman's partitions worked by creating exactly that moment, a small transaction cost and a decision point, and the researchers found that the moment is where people who want to control their eating do so. The moment was there. On some nights you went through it. But it existed, and it never exists inside a sharing bag, and a habit with a decision point in it is a different habit from one without, even on the nights the decision goes the same way.

What makes the second bag easy is where the multipack is. If it's on the sofa, the moment is a second long and the hand is already moving. If it's in the cupboard, the moment involves standing up, and standing up is enough of a pause, in my experience, for the tenth crisp's flatness to register and the wanting to be found already satisfied. Multipack in the cupboard, one bag out. The second bag is still available. It just costs a walk.

And vary the partition, as chapter 21 said. Cheema and Soman found that partitions people are used to stop working. A multipack every night becomes a sharing bag in thirty-gram pieces. A multipack some nights and a bowl on others keeps each one a decision, because neither has become the way crisps are eaten.

If after all that you open two, you've eaten sixty grams, sitting down, with two decisions in it. That's the method working at a lower setting, not failing.