Would this not be being self-taught though? Reading the books for oneself, or deciphering the information on YouTube? Whose doing the communicating hear? It can't be the book or the computer, they're resources not living, breathing people.Those ARE instruction.
Teaching doesn't have to be communicated in person, or with the spoken word.
Not all technique issues involve immediate pain. RSIs often involve irreparable damage over time that only becomes a problem after much of the damage has already been done.
...and upright bass players seem to have a significant issue with this - there is in fact a whole technique book (see: the Alexander Technique for Double Bass) based around this fact.
And I'm not informed enough about the latter information to make a sensible point... So touche my good sir!