Niven’s law was named after science fiction author Larry Niven, who has published them when I first saw them as "how the Universe works". The rules are:

1. a. Never throw shit at an armed man.

   b. Never stand next to someone who is throwing shit at an armed man.

2. Never fire a laser at a mirror.
3. Mother Nature doesn’t care if you’re having fun.
4. Giving up freedom for security is beginning to look naive. (Note: this originally read "F x S = k", signifying that the product of Freedom and Security is a constant.)
5. Psi and/or magical powers, if real, are nearly useless.
6. It is easier to destroy than to create.
7. Any damn fool can predict the past.
8. History never repeats itself.
9. Ethics change with technology.
10. Anarchy is the least stable of political structures.
11. There is a time and a place for tact.
12. The ways of being human are bounded but infinite.
13. When your life starts to look like a soap opera, it’s time to change the channel.
14. The only universal message in science fiction: There exist minds that think as well as you do, but differently. Niven’s Corollary: The gene-tampered turkey you’re talking to isn’t necessarily one of them.
15. Never waste calories.
16. There is no cause so right that one cannot find a fool following it.
17. No technique works if it isn’t used.
18. Not responsible for advice not taken.
19. Think before you make the coward’s choice. Old age is not for sissies.
20. Never let a waiter escape.