Form a mental image of playing drums, as if you were alternating a single drum lick back and forth between both hands. That's not something I find very complex to do, it feels natural to my body. But if I minimize that movement and limit it to a smaller range of motion, such as drumming my index fingers alternately on a desk, I can't really do it rapidly. When I try I end up banging both fingers against the surface in unison. I probably look like an impatient kid banging on the table because his dinner isn't ready yet. I'm not sure why, but I've always had that limitation. which I learned many, many years ago when I was in fact air drumming on a desk in school. I don't know why I can do it with full arm motions easily but not with shorter wrist motions. I've been wondering if that would somehow bleed over into playing piano and I figure the repetition I'm struggling with is related to that limitation.
I feel like there's some body motion that might be the key to this. When I play guitar and get into a strum pattern, I have a bit of a sway to my posture, a nod with my head, perhaps even a tap with my foot. I recall when I first started learning, I was very rigid and strumming felt very robotic. After I became more comfortable with the instrument, I began to loosen up, though it's not something I actually noticed until I reflected. I haven't really gotten that sort of full-body participation going with my piano playing yet. But I'm still getting myself comfortable with the instrument, just the way I did with guitar, so I'm assuming that in a little time I'll overcome this hurdle the way I have all of the other ones that have stumped me when first presented to me.
"So I'll wait for you; and I'll burn"