(“. . . immediate but with calmness.”)
How immediate is instantaneous? Or “What is it that you don’t understand about NOW?” The first question can be addressed to you, the second one to your horse. This is when kinda, sorta, or when I’m ready just don’t cut the mustard. There are a couple of good reasons.
First is the basic nature of your relationship. As I’ve said before, your horse must understand that you are the alpha, that you are higher on the food chain than he is, and that your direction to him is nonnegotiable. Solve that and solve it early, and you will avoid a lot of recurring misery through your years together.
The other reason is more technical. We use our aids in combinations. They amplify and explain each other beyond simple commands or push buttons. They are supposed to work in coordination with each other, and it matters that they are synchronized with the right part of your horse’s strides. If he is late in reaction to one of the aids, that timing is thrown off, and you don’t get the result which is intended.
A few non-dressage terms help explain what you are looking for: You want responsiveness, not just reactivity. In one sense the reaction should be like a reflex, but not like jumping away from a hot stove you leaned on. It must be immediate but with calmness and the horse displaying confidence, not fear. Couple that with his honest intention to please you and not just pay lip service to your demands and you have created the relationship that all serious riders have with their good horses.