Horses can be astounding at times!
I had a big heavyweight hunter at livery with me. This horse was, to put it kindly, a challenge!
He knew his own strength and had, for several years, got away with being nappy. (Barn sour)
I had many hours of challenges with him and truth be known, we came to an agreement but although he never won any argument, he never ceased to challenge me.
That horse would buck for the fun of it yet when ridden by a 10 year old spinabifida girl he was an angel. No buck, he jumped fences including show jumps when I could hardly get him to walk over a coloured pole!
The cross country jumps he would mess around with, taking off to soon or getting in to short, always clearing them by at least two feet, yet with this child he was as smooth and comfortable as he could be.
This is not the only horse I have had this sort of experience with, I caught a friends three year old standing with a foot on each hock of a TB brood hanging onto her tail saying 'Ride now!'
Horses know when they have to be a caretaker. A lot will do it and do it well but others never will.