Sci-Fi writers seem to enjoy coining Laws: adages bearing their own names that live on past their appearances in Sci-Fi stories. Here are five of my favorites, plus one bonus law (actually a Principle) from the world of cartoons.
1. Hanlon's Razor (aka Hanlon's Law)
"Never attribute to malice that which can be adequately explained by stupidity." Ascribed to various authors, including Robert Heinlein. (Or perhaps it was Napoleon, or another candidate.) This law's name is also a take-off on Occam's Razor.
2. Sturgeon's Law
3. O'Toole's Corollary of Finagle's Law
Finagle's Law is a variant of Murphy's Law: Anything that can go wrong, will -- at the worst possible moment. It was popularized by John W. Campbell, Jr., editor of Astounding Science Fiction and Analog, as well as Larry Niven. But the much wackier O'Toole's Corollary of Finagle's Law is:
"The perversity of the Universe tends towards a maximum."
See also: the second law of thermodynamics.
4. Clarke's Three Laws
First law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. Second law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible. Third law: Any sufficiently advanced technology is indistinguishable from magic.
5. Asimov's Laws of Robotics
First law: A robot may not harm a human being, or, through inaction, allow a human being to come to harm. Second law: A robot must obey the orders given to it by human beings, except where such orders would conflict with the First Law. Third law: A robot must protect its own existence, as long as such protection does not conflict with the First or Second Law.
There's also a Zeroth Law.