Those who teach 'real world' techniques, self defense/self protection, hope that their students don't hurt someone outside by accident. They train them to make good decisions, to be good guys and to avoid going to jail ... At least they should.
They also don't want their students to wind up in hospital through some error in the teaching.
It's a huge responsibility.
I live a less stressful life as I teach an 'Art', not self defense, not knife fighting, or combat skills.
Don't get me wrong, I still want the material to be 'real', useful, pragmatic, but have less to worry about as the context I am teaching - dueling with swords - is arcane and not something the bag guys of today feel the need to learn.
It's weird really, I AM on some level teaching people to make sushi out of each other (what was it Rory Miller said of martial arts? That it is 'the manufacture of cripples and corpses'), but the path to flying monkey assassin or down home mugger from 'duelist', is just too big a leap for wannabe gangstas to handle. I occasionally deal with the delusional or the assaholic ... but they tend not to survive the 'request for information' stage.
So where's this going?
Back in the day ... when people really had to deal with bandits, disbanded armies roving the countryside, and political assassinations, numerous 'schools' or security services competed for business, and reputation was everything. Then it was indeed important to ration information until you were certain of the loyalty of your student.
You needed to know that they were not going to steal your secrets and run to your competitors, and you had to trust that they were not spies or informants who could sell you out to an enemy, or perhaps even challenge you and take your students for their own.
Nowadays it is somewhat different. I don't live in a world where I fear that a student will come
back later and use the skills I taught them to kill me. My personal livelihood does not depend on them keeping my secrets or only training with me, and I actively encourage playing and sharing with others to avoid students only learning how to beat people who they know.
The time for withholding information and keeping secrets is gone, and has been for a long long time ..... Why would anyone hold back the meaning behind things any more? After all, there is no 'thing that will make everything work'. No 'secret deadly technique that cannot be blocked'. No magic bullet. These things don't, and never did, exist. And there's no material that can only be taught behind closed doors. Youtube put paid to that.
Really there is only 'Does it work'? "Does it not work'? ..... FOR ME ... And to know that, you need to own what you are doing.
I bet I could show you everything I know. Say it out loud, in words, and demonstrate in slow motion ... and you won't get it unless you, yourself, put in the time. You might think you get it,
but how about I video you and show you what you looked like a bit later. Tell me then how well you think you got it.
If you don't put in the time, you will also never gain the accuracy, the balance, the connectedness and fluidity, that is required to make things work, and your nervous system will not be able to process the rate of data that is being thrown at it when things ramp up to full speed. Your eyes won't see enough to understand what's going on, and your body will be guessing and copying what it should do, not doing what it should do, at the appropriate time.
Right now what I do is mine. I am not afraid to share, because though you may bring new things to the table for me to play with, only time and effort will make what I DO, yours.
I am reminded of that old martial arts joke about the student who is told that when they reach a certain level of black belt, the teacher will come and whisper 'the secret to the system' in their ear. One day, having finally reached that rank, they ask the teacher what the secret is, and the teacher leans in close and whispers ..."Practice" .....