"I eat until I've had enough"

Here's a belief about your body. You eat until you've had enough. Hunger goes, or the wanting goes, and you stop. If the bag's empty, you must have wanted the bag.

Consider what information you have while eating from a bag. You can't see how much you've had. The bag is opaque and it's held at an angle and your hand goes in without your eyes. You can't see how much is left, until there isn't any. You have no sense of the amount at all, from first to bottom, and the only thing a bag ever tells you is that it's finished.

Eric Robinson and colleagues, in 2013, pooled twenty-four experiments on how attention and memory affect how much people eat. One of their findings was about exactly this. When the visual information about how much had been eaten was taken away, people ate more, by a moderate margin, than when they could see it. Not because they were hungrier. Because the signal that would have told them how far they'd got had been removed, and without it they went further.

A bath filling with the plug out, seen from outside the door, is a fair comparison for two sentences. You can hear the tap, and you can't see the level, and the first you'll know is when it comes under the door.

That's the bag. "I eat until I've had enough" assumes there's a signal for enough that arrives on its own, and there is one, faintly, for hunger. There isn't one for a hundred and fifty grams of crisps after dinner, because you weren't hungry, and the wanting that opened the bag was satisfied by the first one, and everything after that had no signal at all except the bottom. The bottom is the only enough a bag provides, and you reach it every time because it's the only stopping point on offer.

The bowl is a signal. You can see it. You can see it half gone and you can see it nearly gone, and each of those is information that the bag never gave you. That's most of why a bowl works, and it's chapter 20.