Horse training can be a relatively mysterious subject to people who have not studied it. Even more mysterious is a behavioral problem a horse has that causes his owner stress and frustration.
What many horse owners don't understand is often handler, not horse, is causing problem.
That being said, that is first consideration in unscrambling horse's ill behavior.
For instance, a common problem riders have is a horse being spooky. In layman's terms, that means a horse is nervous and afraid something is going to "get him". Thus, whenever horse and owner go for a ride it's not usually a relaxing moment.
As a matter of fact, both horse and rider are on edge.
So if we take premise that rider is causing horse to spook, then we must ask, "How is rider causing this."
An uninformed rider may not be aware that perhaps he is sitting tensely in saddle. Also, maybe he's stiff as a board and has a white-knuckle hold on reins.
Believe it or not, horse can sense and feel this tense. When horse is in habit of feeling it then horse's spookiness is also rider's.
Picture it like this. Two deathly scared kids are walking home at night. They both hear sounds and see things. One kid thinks he saw something and nervously asks, "D-d-d-did you see that?" Seconds later other kid hears something and cries, "D-d-did you h-h-hear that?" Together they intensify each other's fears and their anxiety grows leaps and bounds.