You can turn any good horse into a monster. A horse that is unsafe to be around, and it is easier than you think.
Often people reward the wrong things and unintentionally encourage bad behavior. Horses understand appropriate discipline but they will quickly modify behavior to get their own way, accepting treats and rewards for good - or bad - behavior, it doesn't matter to the horse. On the other hand, horses do respond to rewards, sometimes not in the way we want though.
Often people reward bad behavior without thinking. An example: a horse that puts its ears back and acts up when being saddled but gets a treat, not a smack, learns quickly that it gets rewarded for putting its ears back and misbehaving when being saddled. Another example is a horse that is trained to come when called, with a treat, often is excited and rambunctious for the treat but then is inadvertently "rewarded" for that bad behavior too. Behavior that is unsafe for humans, but perfectly acceptable in a herd.
I've often had difficult horses brought to me for training. Years ago I accepted a job working with an orphaned yearling, this young horse had no manners, no boundaries, was extremely demanding and alltogether unsafe. In fact, he was downright scary at times! But he was not "evil". He had been conditioned to behave the way he did because he'd never been taught the herd civilities, no mare had ever disciplined him, not even a mother. So, in his world, he was behaving normally, in a way he thought was "right", but in a way that was extremely dangerous to humans. Consistent discipline and rewards for the right behavior turned that situation around very nicely.
In our world, our equine partners must live with and put up with us, not the other way around. But to achieve this, we must behave in a way they can understand or, in other words, behave as the "boss mare" in a herd. We must reward good behavior that is conducive to the human/equine relationship. Remember, top mares are the leaders in the wild. See you next week! JD