Well, I'm thinking of the observations by Ellis Amdur about how that conditioning can come about after years of ukemi. How the very mindful practice helps develop that sensitivity and conditioning. So we have people with a zillion hours on the mat who can do amazing things. Maybe it was those zillion (appropriately spent) hours on the mat that *allow* them to do those amazing things today. And feel like "hey, it's nothing I developed, I just could do it one day... How come you can't feel it?"
Just thinkin' out loud...