"Is the rider able to ride all the movements with a long rein, long with contact, then as long as possible? It is possible to ride piaffe on a long rein when the rider rides 100% with a balanced body, and the horse is on his aids." ~ Christoph Hess
In the sport of Eventing, ensuring that our horses are truly fit for our level of competition is one of the best ways to prevent unnecessary injuries.
Horses become incapable of learning when they go past a certain level of fear, anxiety, or stress. This means that if you keep hammering away at the horse, trying to teach them something when they are currently overwhelmed with stress, it will not work.
For the horse, the learning happens on the release of the aid. That means if you don't release the aid, the horse will not learn.
"Don't take the tempo down without revving the engine." ~ Chris Bartle