Twenty project management proverbs:

1. You cannot produce a baby in one month by impregnating nine women.
2. The same work under the same conditions will be estimated differently by ten different estimators or by one estimator at ten different times.
3. The most valuable and least used word in a project manager’s vocabulary is “NO.”
4. You can con a sucker into committing to an unreasonable deadline, but you can’t bully him into meeting it.
5. The more ridiculous a deadline, the more it costs to try and meet it.
6. The more desperate the situation, the more optimistic the situatee.
7.  Too few people on a project can’t solve the problems—too many create more problems than they solve.
8. You can freeze the user’s specs but he won’t stop expecting.
9. Frozen specs and the abominable snowman are alike: They are both myths, and they both melt when sufficient heat is applied.
10. The conditions attached to a promise are forgotten, and the promise is remembered.
11. What you don’t know hurts you.
12. A user will tell you anything you ask about—nothing more.
13. Of several possible interpretations of a communication, the least convenient one is the only correct one.
14. What is not on paper has not been said.
15. No major project is ever installed on time, within budget, with the same staff that started it.
16. Projects progress quickly until they become 90 percent complete; then they remain at 90 percent forever.
17. If project content is allowed to change freely, the rate of change will exceed the rate of progress.
18. No major system is ever completely debugged; attempts to debug a system inevitably introduce new bugs that are even harder to find.
19. Project teams detest progress reporting because it vividly demonstrates their lack of progress.
20. Parkinson and Murphy are alive and well—in your project.

Source: Project Management: A Systems Approach to Planning, Scheduling and Controlling by Harold R Kerzner (11th Edition).