Long discussion with my dressage instructor about horses learning how to learn. Some of them do figure out the learning concept and they do some fairly impressing analysis, especially when they are back in the pasture for the evening. This week we spent a few minutes teaching Gracie how to come to the whip instead of move away from it. Weird concept, but she got it as soon as we applied treats to the problem. Then the next day when I asked it was there immediately. She had clearly thought about it overnight. She has thought her way through the idea of Piaffe and, while she finds it ridiculous, she is willing to give it a try.
My other mare just shuts down if you ask her to try something new that she thinks is too difficult. You then have to go back to something she finds easy and build up to the new thing very slowly and from another direction. I am pretty sure there is a teaching lesson in both those horses.