Jencel’s principle of triviality: any self-consistent system of knowledge can be reduced, at least theoretically, to a small number of clear elementary postulates and what follows from them. So, any system for which it is not immediately clear what these postulates are, is not self-consistent.

Simply put: if you cannot explain the system using very elementary language and constructs, then there is probably inconsistency in it somewhere.

Example: most religious doctrines.