Harry Whitney is a fantastic teacher of horses and humans. I've had a lot of teachers of all sorts of methodologies and temperaments and Harry is quite possibly the best, and definitely in the top two. He is a very subtle and sweet person.
I just saw the movie "I Heart Huckabees" last night. Harry is a little bit of an existential detective. The horses help with the existential part. The thing about horses is that they don't care much about all of the stuff whirling around in a human's head. And yet you have to create a relationship with a horse if you are going to be a competant horse person. So you have to build a relationship that is non-verbal, non-symbolic. It is not structured by the cultural apparatus that usually structures relationships between humans. This can be quite challenging, especially with a creature that is 6-10 times one's size and their own hard-wired view on what is important in the world.
Horses understand the world on gut level, in a very simple but also very honest way. For instance horses do not care one iota about money. This is very important to most humans, structures our relationships with each other a great deal of the time. Horses don't care about money but they care about the relationships which money sometimes represents, and that is leadership. Horses always want to know who is in charge, who is going to be responsible for the situation. If they feel that their rider is not on top of things, then they are going to fill in. Which is the reasonable thing to do. The heart of some of the more traditional approaches to horsemanship (and leadership) is to break that idea of taking over right out of a horse (or human). In very blunt and sometime brutal ways a horse is shown that it has no power any more, even over it's own life. This simplifies the relationship between human and horses quite a bit. But it certainly is not very pretty. But it works. And sometimes it's a better deal for all involved to have things real clear like that. But of course it pretty much kills all the joy out of all involved.
There are other options, but their a lot more difficult. That's where Harry and people like him come in.