It is said to be a tradition that originated hundreds of years ago and it is because the horses were mounted by soldiers who carried long swords.
It is believed, moreover, that the left eye of the horse is the eye ‘quick reaction’. Then when a stimulus is presented by the left side, that eye will produce a reaction faster than that of the right eye.
There is another version that suggests that horses tend to favor their left side, in general, possibly due to the way they were in the belly of the mare.
Now, we must be clear that the horse has independent vision in each eye, seeing different things on each side, so many times they want to turn to see what happens on the other side.
Most coaches indicate that the horse is suitable to be ridden and driven on both sides and that both are developed equally.
If we find an equine that only responds on the left side and we are interested in acting on the right, we must perform a series of exercises and regular practices to work on its other side.
We have always been taught that the horse must be entered on the left side, take the branch on the left, ride on the left etc …there are many reason for this.