One Track Mind
Perhaps the best way to sum up a horses mind is to refer to it as a one track mind. A horse uses each side of its brain independently to take in stimulus from the environment. Therefore, each side of a horse left or right, near or offside wants to focus on one thing at a time. A horse will tend to balance each side by rotating to the other side in order to relate to the same sensory information. This is why a horse with proper training is conditioned on each respective side until they are 'right on' or balanced to carry themselves properly with the rider. A horse will often respond on each respective side very differently. As a rider you need to allow the horse the little time it takes to relate to things on both sides. Then the horse has cleared its questions and can then focus on your natural aids to guide it along. The result will be that your intentions become crystal clear to the horse.

You really get a two-track mind in a horse when it is scared or confused. It is reacting and questioning at the same time. Whereas, if a horse is content, focused and hooked on either side to pressure or a situation then in can follow through in a concentrated manner. For instance, if you kick a horse to go with both legs at the same time, this confuses the horse (especially a Colt) and the horse will eventually quit reacting to ther mixed messages. Response is a independent focus to a single aid, reaction is a scattered focus to many things that usually produce nothing.

Why A Horse Kicks
Nature has provided all animals with some means of defense. Kicking is the horse's natural method of defense (however its flight response should prevent this from ever happening.) In a horse's natural state, biting and striking may be the introduction to a battle, or small difficulties may be settled with the forefeet and mouth, but the principle battles are fought with the hind feet. As we know the horse, has no more need to kick than a cow to use her horns. But, the fact remains that there is an number of horses that have this habit.

The causes for kicking are numerous, but may be reduced to two. The first is the disposition of the horse. They have the instinct of self-defense developed so highly that at the least indication of danger, or mistreatment they defend themselves. They seem to kick at almost anything. The habit grows to such an extent that it becomes easy for the horse to kick, until we say it has a "Disposition" to kick. Because it has this disposition is no reason for classing it as an outlaw and thinking it cannot be handled. Its natural tendencies will only require more patient and timely effort to make it (like) any other type.

Most horses do not kick on account of a bad disposition, but because (of the second reason) their owners really taught them to kick by poor management in colt training. Every horse that becomes a kicker does so in self-defense. Of course, after the habit is repeated a few times it learns it's power... there are two things necessary to fix in the mind of the kicker. First, submission (give to pressure). Second, the horse must learn that whatever caused him to kick will not hurt him...Rough handling is injurious and does no good. (Professor Beery's Illustrated Course in Horse Training. Book No.3. pp. 1-10.)

Horse Problems
Curing a horse's problems is simply a matter of backing up and retraining him the way it should have been done in the first place - a matter of replacing bad habits with good ones. [The trainer has a difficult job of undoing before the doing can occur in the horses training.] The trouble is re-training a horse is four or five times harder than doing it right in the first place. Mostly it is a case of staying alert to be ahead of the horse in every move he makes so you can use the proper signals to get the proper response and then give him reinforcement as a reward. This is good communication... There are many things that discourage a horse from going forward. Some riders train their horses to piddle along by constantly slowing them down with the Reins. But the biggest discouragement comes from the stiff rider with hands that constantly jerk the horse's mouth. Today's style of seat in western must have been invented by a non-rider... This stiff unyielding seat assaults the horse's Back and makes him reluctant to move forward willingly. The Wild West Syndrome is the do-it-or-else training method... These people soon find themselves with a hooligan by the end of the halter. (Twelveponies, There Are No Problem Horses, only problem riders, -20)

Dressage - A System of Basic Training
Most horses are stiffer on one side than the other, which means they resist more to one side than the other. Therefore they are slightly more bent (or softer) one way, because the muscles are shorter on the softer side than the other side. In order to get the horse going balanced, the muscles on the short (soft) side must be lengthened, so as to be the same as those on the resisting side. (The hard side is usually the Mane side. Most horses are hard to the right and are thought of as left sided like us being left handed with the mane hanging on the right side.)

In considering balance and collection; balance comes before collection. Unless the horse works balanced he cannot be collected. The head and Neck form the balancing pole in weight distribution. It is by their position that a horse carries his center of gravity forward or backward. A young horse, when at liberty, naturally learns to balance himself. When the horse is mounted this balance is upset and the center of balance is displaced. Balance is acquired by developing the muscles, especially the hind end and back, by exercises... Collection is the concentration of the horses energy, when the whole body is collected into a shortened form with a very light rein, with even more active hind-end movement so that he has the maximum control over its body and is in a position to obey instantly the slightest aids of the rider... The rider must never attempt to pull the head up with the reins, as the result would be a false head-carriage with the top line in a concave position... The rider must use his legs to push the horse's head up by making the hind-legs more active... A horse must look to the way it is going (and) the horse must change the bend to the way it is going (unless doing a counter bend or dressage exercise)
(The Manual of Horsemanship of The British Horse Society 1936, 1-26). And, remember it is the method and the person, not the place, that trains the horse. (Cutting, Bill Freeman p-100)