You just mentioned that the one guy just couldn't "get it." Well when I used to teach SCUBA,, we had students who often just didn't quite get it easily. One glaring example that taught me a lesson as an instructor,, was a very intelligent guy who just didn't "Get" part of the class.
Separate, special one-on-one instruction wasn't helping.
UNTIL,,,,,,,,,, I changed terminology.
Then it all fell into place. Sometimes something as simple as changing terminology makes a huge difference.
BTW;; I think it was my description of motor memory, not Mobuck.
All good!