From Murphy's to the Pareto: Famous 'laws' that are not on the books but rule the world

You've probably heard about Murphy's law, but what about other eponymous laws? An eponymous law is a principle or rule named after a particular person. Sometimes named after the individual who coined the law, in other cases it was named after the work or publication of an individual. They often have a backstory of great significance.
From Murphy's law to the Pareto principle, let's check out some notable eponymous laws that rule the world in this post!
From Murphy's to the Pareto: Famous 'laws' that are not on the books but rule the world