The Five Rules of The Peter Principle Progression:

Rule 1. Occam’s Razor: The simplest answer is usually the correct one.
Rule 2. Hanlon’s Razor: Never attribute to malice that which is adequately explained by stupidity.
Rule 3. The Peter Principle: [In a hierarchy] Every employee tends to rise to his level of incompetence.
Rule 4. Grey’s Law: Any sufficiently advanced incompetence is indistinguishable from malice.
Rule 5. See Rule 1.