In some instances, you have to use a correction appropriate to the situation. If a horse tries to flick it's head at me and hit me with it's jawbone, I will make sure that the horse runs into the palm of my hand. This is a correction that a horse understands. Horses in the wild think nothing of using their jawbones, shoulders, feet, and bodies as weapons. They undestand what it means for another horse to use its head and jawbone as a weapon.
Horses are herd animals, they understand things differently.
The worst thing that can happen to a herd animal is to be sent out of the protection of the herd on their own. In the wild, a horse that acts out will be sent out 100 yards or so from the herd until they have learned their lesson. This is severe punishment to a horse. On their own, they are vulnerable to predators. In the herd there is safety in numbers.