Good dressage is not about force, about the consciousness acting with nobility to control or modify the unconscious instinctive reactions. Genuine dressage relies instead upon increased awareness and insight to allow us to make positive choices in working with the horse.
Education in dressage is then the cultivation of understanding the dynamic structure of experience and the consequences of actions via the aids which leads to the recognition that every experience of any kind is an opportunity for healthy practice with the horse.
We build a language in which we communicate and in which the horse can communicate with us. Working then with the horse/human physical and mental state, we build a bridge which brings about a relationship based in harmony.
All of this may seem philosophical and theoretical, but good instruction is the process of turning these ideas into a practical practice. Working with the horse is something which must be done every day if possible. Short sessions are always better than long one. It is about quality rather than quantity.
Sadly, it is not likely that you will find an instructor who will mention, no less work on, this subjective level and so it for each of us individually to attend to this level. No one can train you as well as you can train yourself. It is about mindfulness and awareness in the practice with a constant sense of simplicity and kindness not just toward the horse but toward yourself.
Who in their right mind takes on this kind of training? Only those whose love of the horse and whose fearless nature will take on the greater challenge of self awareness.