Why stopping seems sensible

Nobody stops a medicine for no reason. Stand in the reader's kitchen and the reasons line up, and I want to give each one its due before the book starts arguing with any of them.

You feel better. That's what the medicine was for, and it's worked, and continuing to take something for a problem that's gone feels like wearing a plaster after the cut has healed. Or you feel fine, and you've felt fine throughout, and a tablet for a thing you can't feel is hard to keep believing in. You missed a day or a week and nothing happened, which looks like an experiment with a clear result. You don't like the idea of depending on a chemical. The side effects are real and unpleasant, and the illness they're treating is invisible. The doctor was brisk and never said what would happen if you didn't take it. And the tablet is one more thing in a morning that already has too many things in it, so it drops off the list the way anything without a consequence drops off a list.

These are honest. Research on what people believe about their medicines finds the same two forces in most of them. In a study of 324 patients with four different long-term conditions, Horne and Weinman found that most believed their medicine was necessary, but over a third also had strong concerns about it, mostly about dependence or long-term effects. When concerns outweighed the sense of necessity, people took less of it. A later review of 94 studies pooled that pattern across more than 25,000 patients and found it held. Nobody in those studies was careless. They were weighing something, and the weighing came out against the tablet.

So the habit isn't stupidity and it isn't defiance. It's a reasonable person using the only instrument they've been given, which is how they feel, to judge something that instrument can't measure. The next chapters go through the beliefs one at a time. Most of them are half right, and the half that's wrong is the half that matters.