The environment. You're out of the house, you don't want to do things by halves. The first-class room. The state-of-the-art equipment. The loud music. The trainer's encouragement. All these elements combine to push you to work harder than if you were alone in your living room or basement.
Motivation. You've made an appointment, and already that's enough to keep you from skipping a workout you know will be demanding. At home, there are a thousand distractions and moments of cowardice lurking around the corner, threatening to push us into doing something else. By going to Cartel, you make sure you make the best possible effort, because you don't want to be unnecessarily out of place.
The ripple effect. Everyone suffers with you, at the same time. Despite the music and the sound of the rollers, you hear grunting. Out of the corner of your eye, you see faces disfigured by the effort. By forcing together, all the members of the group feel they are participating in a kind of common struggle. We encourage and congratulate each other. Peer pressure is a call to give it your all, as if it were also a question of respecting the seriousness of others' efforts by applying them to your own.