Why are some people lazier than others?

We’re used to health warnings that urge us to do things that we don’t really have a great urge to do: to exercise more, to eat five or eight or even 10 portions of fruit and vegetables a day. But for once the official advice sounds easy; loaf on the sofa, binge-watch box sets, stay at home. This all sounds as though it should appeal to our lazier sides.