This may wander a bit as I am just thinking out loud, but I recently had one of those epiphanies where you think, How have I not known that? Or in my case, how have I not been able to feel that?
I've been riding with Chemaine Hurtado, owner and trainer at Symphony Dressage Stables, for several years now. While she does come up with new stuff all the time, there are some things she has to say over and over and over. Deeper and rounder are two such things. In fact, not long ago she felt compelled to clarify that deeper and rounder are the same thing. She must have felt the need to explain it that way because Speedy was obviously neither of the two, indicating that my comprehension was lacking.
I don't remember the exact moment that it happened, but one day, I heard Chemaine's voice in my head say flex him to the inside to put him on your outside rein. At that moment, I felt something physically click into place. The bend isn't for the bend's sake. It shapes the horse's body so that the horse can move the way we want him to. Inside bend and outside rein are my new holy grail.
Think about it, how crucial is it that our horses be on the outside rein? It's everything! That's how you get a half halt. That's how you get haunches in or a turn on the haunches or a canter depart. And since the layers go on and on, I know that there must be even more that I'll be able to get from my boys when they're actually on the outside rein.
The thing with finally internalizing the idea of getting a horse on the outside rein is that it leads to lots of other ahas! like getting the horse even on both reins. I knew what that meant, but like the idea of inside bend, I didn't know it in my bones. It was more vague; something I was trying to create. Now, I get it; I feel the unevenness and work to get my horses better balanced between my two reins.
That's both the frustration and beauty of dressage. There is always, always more to learn, and even when you get it, eventually, you'll find an even deeper understanding of a concept you thought you already understood.