From the Horse’s Point of View
H orses don’t have a reason to care if they are engaged and they don’t see a reason for increasing the bend. They don’t try to be bad, but it’s natural for them to take the easiest path and try to remove the difficulty by leaning one way or the other.
Even the best-trained horse in the world doesn’t do a quality shoulderin automatically. The best-trained horse answers the aids sensitively and with suppleness, but he doesn’t do it by himself. Even if you have independent aids, swinging hips, elasticity and all the other things that make you an exceptionally skilled dressage rider, you’ll still have a horse that wants to take the path of least resistance, such as getting shorter and quicker, running through the hand or falling left or right. The horse will take the easier path until the rider is able to direct the energy the way she wants it.
My analogy is this: Water is always going to flow around a rock in a stream unless there’s a little dam to make the water go over the rock. I think of the water as your horse’s energy and the rock as your horse’s withers. The energy will always fall to the left or the right of your horse’s withers—more on one shoulder or the other—instead of going straight over and through the topline. Your aids need to create the little dam that sends the energy straight through your horse’s topline.