What a fascinating thread. I've always said that Bill gives great thread.
I think "understanding" changes over time. The example given, the upper body block. That was the very first Martial technique I ever learned. It was in Greek Gojo-ryu/Pankration. A year later, when I first took up American Karate, the same technique (in this new school called a rising block) was also the first technique I learned. They were slightly different as the Goju one had an "initial protector" (which I liked better.) Over the years I've trained different disciplines, most of which have the same, or similar, rising blocking motion.
As a yellow belt (I always thought that was a strange color for a Martial Arts belt) a boxing gym opened down the street. For some reason, I felt threatened and started to prepare to fight boxers. Every night after class I stood in front of the mirror throwing rising blocks to stop a boxers punches. (Hey, I was a teen and it was right after the sixties.) I had, what I considered, a decent understanding of that rising block.
A few years later, I told the guys in that boxing gym that story, we all had a good laugh.
So....about ten years ago, during a summer where I went to a lot of Martial Arts dinners and get-togethers, I asked a lot of instructors if they had ever actually used that block in a fight or in sparring. Most were Okinawan, Kenpo, Tae-kwon-do, Tang Soo Do, American Karate or Shotokan Instructors. I asked about thirty of them. None ever had. They were friends and I believe them, I never had either. I'm quite sure other people have indeed used that block in fighting, just not anyone I know or ever saw.
Although I don't think it applies to actual fighting, at least as I know it, I'd probably still teach it today if I was still teaching beginners. Why? Because in tandem with other blocks in a hard blocking set, it teaches "areas" - as in areas of the body and head to protect in blocking. It's also a great intro to students as to why the baby finger side of the hand is always up. I've found this sparks their interest in body mechanics more than any other technique at a beginners level and causes them to retain these things better out of sheer curiosity.
So, my "understanding" of that technique might be different than somebody else's. I think the term "understanding" differs based on a lot of contributing factors, one of which is experience. That does not mean either of our understandings is better or worse than the other.
Dominique Bouhours (1628-1702) French Jesuit priest, essayist, critic and grammarian, while prone on his deathbed, said to one of his students "I am about to - or I am going to - die: either expression is correct."
I think "understanding" might be that way, too.