The first nine minutes of this video is an excellent lecture by Sensei Bob Rea on what he calls zones - what I've called "edge."
In a nutshell, Bob says that there are different states of being, or "zones" that uke and tori (and even attackers on the street, etc...) can be in.
- We can be in a SAFE ZONE, where we are comfortable and competent and not at any significant risk of stress or injury, and that is a good place to operate, but not much learning goes on within that SAFE ZONE.
- We can stretch ourselves and get into a LEARNING ZONE, where we are less comfortable and have greater risk, but we have maximum potential for learning.
- Beyond the LEARNING ZONE is a PANIC ZONE. This is a self-defense type situation in which we react instinctualy to protect ourselves. No learning goes on in the PANIC ZONE.
- And beyond the PANIC ZONE is what BOB calls the TWILIGHT ZONE - the place where dragons live. Being in this place scares the hell out of everyone involved and nobody ever wants to go back there once they've peeked across the border.
This is similar in some ways to the classic color code system for self-defense, where you have GREEN, YELLOW, RED, and BLACK alert conditions depending on where you are and what is going on around you. It is also similar to some stress theory that postulates an inverted-U shaped learning curve where low-stress is non-productive for learning and high-stress is dysfunctional so you want a moderate level of stress.
What I think is interesting, is it is possible to expand and contract your boundaries (your EDGE). If you lie on the couch in the dark all the time, the edges between SAFE and LEARNING and PANIC will contract, but if you regularly approach your edge and look around at what happens at the edge and maybe peek over the edge, then you will expand your boundaries. Some of your LEARNING territory will become SAFE for you and some of your PANIC territory will become a LEARNING ZONE. You don't have to leap past your edge to expand your boundaries - just approach them regularly and systematically.
I also really, really like his brief discussion late in this lecture about how the instructor or leader or higher-ranked player in a pair needs to be able to read his own state and that of his partner, and he needs to be able to protect himself (stay out of TWILIGHT and PANIC ZONES) while working to move both partners closer to that edge between LEARNING and SAFE zones.
I agree, that is an extremely valuable skill - perhaps one of the 2-3 most valuable skills to learn in judo and aikido - de-escalation.