Taking part 2
for example, the uke is maintaining a light perpendicular push into nage and adjusting with his circular movements. Nothing about nage's movements compels uke to do so.
I had two big surprises with Gleason Sensei last August: first is that he's so small. Second is that he's so strong.
I did the very exercise linked above with him and his movement does compel. The effects on uke are the result of his keeping a steady, light pressure on nage while nage moves.
It's not to say uke couldn't do something else, such as withdrawing the push, etc., but he has to have a reason to do something different. He has to feel that something is not right and that he has to withdraw, but in this case, he doesn't know what he feels. It's a very disorienting feeling to push on someone Gleason Sensei's size and feel that you're pushing on a post in the ground.
Likewise, when I took Rob John's wrists in suwari waza, I got zero sensory input when he raised his hands. I was trying to hold his hands down and he just went straight through my strength with no feeling of effort from him. And if he'd simply brought his hands back down, he could have given me whiplash because I could not have let go because I could not feel what he was doing.
The startling part about "it has to be felt" is that there's so little sense of effort behind powerful effects.