Why Horses Blow Up

"...their training approaches seemed to be going so well, then the horse suddenly lost all his composure. Oftentimes their first assumption is that they did something terribly wrong or that the horse had some kind of psychosis or other significant behavior problem. In most cases the reality is that these horses are simply blowing off stress. It's something that a horse sometimes just has to do. Once the handler understands the process as well as the signs that the horse will likely exhibit that a stress release is imminent, this stress can be released safely and not devastate the gentling or training process."

http://www.kbrhorse.net/tra/blowup1.html

A site that says it better than I could ever say it myself...I still feel that the Parelli Natural Horsemanship (PNH) methods are more effective than the way in which these individuals train (naturally, with clicker training infused), but they have some great theories, ideas, and thinking that accurately explain a horse's psychology. As far as equipment goes: no, you do not have to use the PNH-specific equipment. However Pat Parelli has discovered, refined, and created his tools with the ultimate goal of the most effective communication possible between horse and human. Without the equipment, you can still accomplish the same task...but it does take longer and requires more effort. For example: the lead rope and halter. The halter is thinner and lighter than most rope halters and thus is harder for the horse to lean against; in this way we start to teach the horse to release to pressure rather than lean through it, which they are naturally inclined to do. A web halter permits and even encourages horses to lean into pressure because it evenly distributes the pressure over the wide band: think of how a harness is made - you would never have a horse pull a harness using thin ropes but instead distribute the weight and pressure of the cart against wide bands of leather. Also, the knots are placed in specific areas that further encourage the horse to give to pressure rather than fight against it. The clasp on the leadrope is designed to hold a horse pulling back to a specific weight, then it will break (for everyone's safety). It also provides a weight, moreso than your average shank, that indicates better to the horse your actions on the leadrope ie. when you lift it, when you wiggle it, etc. The leadrope is a heavy yachting rope that is heavier than most, if not all, leadropes in existence, and yet that is also very soft and supple. This allows it to instantly release to a horse's give to pressure, providing the appropriate release, and thus reward, when a horse "tries". Also, its length allows one to use it for "games" with the horse, encourages horse responsibility in said "games", and gives you the legth to play, regardless of what occurs. One last point. If you think that you shouldn't have to buy equipment with which to play with your horse: do you not already do the same for any other "method" you use on your horse? What about bits? Martingales? Tie-downs? Nosebands? Halters? Bridles? Leg wraps and boots? Spurs? Crops and whips? All your current training tools were purchased specifically by you, for your own training purposes, so what, really, is the difference?

Does natural horsemanship take time? Of course it does!! But what training method does not?! What is an extra 10 minutes (or longer, should you choose) working on the ground before you ride if it creates a quieter, more responsive, safer horse, and a true partnership?! What would you say to investing a little extra time on the ground if you never had to deal with another vice such as bucking, biting, rearing, kicking, (etc) again?

A couple of extra sites that help us understand better how a horse works:
http://iceryder.net/brainworks.html
How a horse's brain works, from a biological p.o.v.
http://www.usyd.edu.au/su/rirdc/articles/miscell/sight.htm
How a horse's vision works (ie. corpus callosum...)