Berkeley's Laws: (laws) 1. The world is more complicated than most of our theories make it out to be.
2. Ignorance is no excuse.
3. Never decide to buy something while listening to the salesman.
4. Information which is true meets a great many different tests very well.
5. Most problems have either many answers or no answer. Only a few problems have a single answer.
6. An answer may be wrong, right, both, or neither. Most answers are partly right and partly wrong.
7. A chain of reasoning is no stronger than its weakest link.
8. A statement may be true independently of illogical reasoning.
9. Most general statements are false, including this one.
10. An exception TESTS a rule; it NEVER PROVES it.
11. The moment you have worked out an answer, start checking it -- it probably isn't right.
12. If there is an opportunity to make a mistake, sooner or later the mistake will be made.
13. Being sure mistakes will occur is a good frame of mind for catching them.
14. Check the answer you have worked out once more -- before you tell it to anybody.
15. Estimating a figure may be enough to catch an error.
16. Figures calculated in a rush are very hot; they should be allowed to cool off a little before being used; thus we will have a reasonable time to think about the figures and catch mistakes.
17. A great many problems do not have accurate answers, but do have approximate answers, from which sensible decisions can be made.