You sit right over the horse’s center of movement. You sit right over the horse’s center of gravity. You sit right over the horse’s weakest and therefore most sensitive area, the middle of its spine. Your seat has a strong influence on the movement of the horse for those reasons. GOOD OR BAD! For this influence to be good your horse must trust your seat enough to relax the back muscles and allow its back to swing. Your horse will only do that when you prove to it again and again that your hip will swing along with it. Then, and only then, will the horse allow you to influence its movement with your seat.