First off, there is a body of knowledge, and finally, it gets documented and taught and lectured upon and such is indeed done by the first hand practitioners who know exactly what they're talking about, because they have done the knowledge, they have seen the knowledge, they have been to the knowledge. Those who do this are the masters of the knowledge, and they show this by what they can do.
In time there comes a following generation, and that following generation takes two forms.
One form takes what the masters have done, pokes at that, experiments with that, sees personally how it works, and in time can show that everything that of the masters have done and taught, they too can do and teach. This form has reached what's often called the journeyman stage, or the college equivalent of a master's degree. The next step from there is to take that knowledge, to twist it, to invert it, to work with it sideways, to expand, extend, stretch, and to do so in a manner that can and does get explained, taught, passed on, and in doing so, that person demonstrates being an actual master, the college equivalent of a Ph.D.
The other form that the second generation takes is the most popular and most widely practiced, and itself results in succeeding generations. This is the form where the wannabe master pointedly refuses to bother with the waste of time of doing all that study and work and understanding, and instead jumps to announcing that one is a master and that one is the supreme, and all others are just wannabes and not that capable or, mainly, not as important. A couple of facets of this are that the wannabe master absolutely can not get questioned, only obeyed, and that the wannabe master often is at least louder or more firmly entrenched than those around . . . .
This second form and its practitioners tend to quickly disappear into an acrimonious and shrill haze of I'm the master, y'all stole that from me, y'all are just copycats, y'all must bow down, I didn't steal that, it's called sampling because I'm a master and I don't have to Do anything, I'm a master . . . Etc.
Going back to the first form and its practitioners, this is the form that regularly stops a master---and particularly a master---in his or her tracks and gets a statement of "Ooooooooohhhhhhhhhhhh. I Didn't Think of That One . . . Master, teach me what you just did, so that I may do that as well."
And with no screaming, no histrionics, and most importantly, no lies, the recognized, undoubted, and acknowledged master then teaches the recognized, undoubted, and acknowledged master . . . and anyone else who has the relative balls, ethics, and actual backbone to just study, learn, and practice, and document that practice for the next person to come along.