An interesting question, Don.
As I've had two 'career paths', so to speak, in the martial arts (one pre-accident and one post) I have two answers.
Both are similar in a way.
My first class of Lau Gar, I was run ragged by all the physical warm-ups (despite my being in very good condition at that time). Then our instructor introduced us to the delights of stretching and the splits

!
He had us try to get as low as we could, which was not very low for most of us (ROFL) and came around the class inching peoples feet out wider still. He got to me and I reckoned I couldn't possibly get my feet any further apart so, as he went to stretch me that little bit more, I said something you should never say to a martial arts teacher ... "Don't you dare!". He looked me in the eye and said "You're always capable of more than you think you are" and hoiked my feet a few inches further apart.
Nowadays I would consider that to be a little reckless, after all, altho' I was very fit, I was also not very flexible and he could've popped a tendon doing that to me. At the time tho', that homespun philosophic line did the trick. I was hooked and until an Audi tried to kill me I never thought there would be a day i wasn't training.
My experience with MJER was similar in that it was finding that my determination exceded my body's limits that told me I was on the right path.
In this case, it was finding at the end of a three hour class that the white karate gi I'd bought only four hours before now had red knees. That proved that all that wincing I'd been doing wasn't just me being a jessie as I got my introduction to fighting movements in seiza and also proved that I might be educated but I can also be very stupid sometimes

. There's a reason why knee pads are worn for Iai :lol:.