Before the onset of modern medicine, people seeking help in particular domains sought out the authoritative advice of shamans and witch doctors to help cure their ailments. These experts were of course, full of remedies, and sometimes they worked and sometimes they didn’t. No one could quite explain how or why they worked (especially them), but insofar as they did, they weren’t granted too much scrutiny. When they didn’t, it was chalked up to the mysterious ways of the domain. This phenomenon is what the great physicist Richard Feynman called “cargo cult science.”
The primary conduit of the information which informs these experts is an oral tradition and history within their community. In particular, there is very little written record of the practices and history of their work, and their certainly isn’t any scientific analysis comparing the techniques they often employ and their effectiveness. They often have rather strange methods which are enforced strictly by their senior members, although it’s never quite clear why these conventions should persist.
This leaves the source of their authority as simply the time they have spent there. It also helps facilitate a perverse incentive amongst them, which is to maintain the obscure and impenetrable nature of the tools they use for the domain they have colonized. This creates a hostility to any attempt to introduce a systematic approach to their practice, and they typically swiftly stall or destroy any and all written records of how they constructed what they have built over the ages, thus protecting the wisdom they are sitting on.
Beware of documentation by folklore.