In equestrian sport there is one thing specifically that tells a lot about the quality of riding, namely the horse’s mouth. A contact that is pleasant and practical for both parties is a skill and accomplishment that is the essence of riding.
Sometimes a horse behaves in ways that humans find incomprehensible or surprising. The thing which guides a horse in its behaviour, regardless of the situation, is always what, from the horse’s point of view, is the most rewarding or beneficial to it. In efficient training the trainer uses the things the horse considers rewarding as reinforcement.