The mystery magic is exactly in the "mentally easier" part. The amount of calories one is comfortable eating largely dictates their weight over long enough time

The mystery magic is exactly in the "mentally easier" part. The amount of calories one is comfortable eating largely dictates their weight over long enough timescales. Most people on restrictive diets fail, because over the long term discipline is really hard. On the other hand, most thin people aren't that way out of some conscious commitment to being so, they just don't choose to eat as much as heavier people do. So the mystery of weight management isn't in managing caloric intake, that's simple, but difficult. The mystery is in managing hunger, which is complicated, but easy. For an example of this, addictive appetite suppressants are really effective at weight loss. This is... less than ideal, so people aren't typically encouraged to pick up an methamphetamine or nicotine or cocaine habit for weight loss. But they work, and compared to discipline diets easy to follow. Ideally, we find appetite suppressants that don't have substantially worse side effects.