The stronger the grip the more force and direction you get to work with... the less someone wants to stay strong and not move their feet the more they tell you where they are weak. Whether tori listens to the uke instead of trying to do something to them is another thing.
I got bumped from my flight to Dallas due to weather and I just got home awhile ago and saw this post. I goofed...
It should say "the MORE someone wants to stay strong and not move their feet the more the tell you..."
If someone is resisting strongly as Michael Hacker was describing, the only possible way they can resist is to use force to resist kuzushi and then you do hando no kuzushi (translates to something akin to "reactionary kuzushi"). If the uke is giving any force (repeat ANY force) it can be turned into kuzushi that works.
I personally am not worried about attacks that have NO force.
I'm off to Dallas again tomorrow for a weekend koshukai with a bunch of our folks. Looking forward to lots of people putting force on me!