When I was in high school, a friend who played drums in a band would try to pull off these super complicated fast fills. He couldn't pull them off and I always thought, "why doesn't he play something he can get right?" Well, after months of practice, he was able to pull them off. He was a great drummer, but he worked at incredibly hard to get there. It's a little tangential to what you said, but it feels appropriately related.

I guess I'm agreeing while also saying that you can get there by failing a lot at full speed first. Maybe he practiced at half-speed when he was alone and I never saw that part.