1. TANSTAAFL: There ain't no such thing as a free lunch.

2. Incentives matter.

3. Economic thinking is thinking on the margin.

4. The only way to create wealth is to move it from a lower valued to a higher valued use. Corollary: Both sides gain from exchange.

5. Information is valuable and costly.

6. Every action has unintended consequences.

7. The value of a good or service is subjective.

8. Costs are a bad, not a good.

9. The only way to increase a nation's real income is to increase its real output.

10. Competition is a hardy weed, not a delicate flower.

via Ten pillars of economic wisdom.