Re: Questions re: mistaken presumptions
I remember somewhere in one of Saotome Sensei's books he said that all of the movements and principles are natural and things that we all do in daily life. The problem is when put in a martial context, we get scared and start to act un-naturally. With that in mind, I generally do two things. One is to remind students of situations in which they already use the idea.
For your example above, I might talk to a student about how they go through a revolving door, the push is to the front, but it is directed toward the door's "center." This kind of metaphor explanation seems to be helpful.
The second thing I try is to develop actions/activities where the element of fear is taken out. Basic techniques/movements that culminate in a stretch rather than a throw have worked well for me. Then once I see that students are entering and connecting well with their partners, then I progress to doing the previous movement with a throw or pin.
There are a million ways to relax students, I've found. I don't feel that verbal explanations necessarily mean that I can't physically demostrate a principle (I hope!) For me, they are a valuable tool. As you know, although Endo Shihan doesn't talk much at Honbu, he does talk a bit at Saku. This has helped me a lot.
Now, what is interesting to me is how and why this general problem of a lack of understanding has arisen. This is probably quite pessimistic, but I feel that there is little real progress and development in the Aikido world. I believe that many (most?) instructors and senior students are not actively progressing and unconsciously sabotage their students by not finding the best way to help them. This leads to a misunderstanding of concepts like center.