|M. during her lesson having a taste of Aspire Development level (schooling of the horse)|
They say "feel" is the most difficult aspect to teach but I find that most riders can learn that "feel" - what I personally find challenging (in a nicest possible way) is to teach timing and the ability to act on the feel.
When focused yet relaxed, most riders feel the movement and after practice and observation, can tell me exactly which leg of the horse moves, whether it is in the air, pushing off, reaching forward or perhaps going sideways. Most riders, even with eyes closed and on their first lesson, can tell me when each shoulder of the horse moves simply by feeling it through their thighs and knees.
They feel whether the horse's ribcage bulges more one way or the other and whether the horse's way of going makes it easy or difficult to remain symmetrical through upper body.
Feel might not be easy but it is rather teachable.
Now, timing and ability to act on the feel comes with so many trials and errors, emotions (frustrations being one I see most), tension, trying-too-hard...
Good timing (of aids/communication between rider and the horse) makes movement look easy. Great timing makes movement look magical :)