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- "If something cannot go on forever, it will stop."
- Herb Stein's Unfamiliar Quotations 
- "I belong to the don't-know school of economics."
- "Economists are very good at saying that something cannot go on forever, but not so good at saying when it will stop."
- These quotes were a typical reply to those arguing for urgent fiscal policy measures to address the widening U.S. account deficit in the 1980s, and a reminder that knowing if and when to act in macroeconomics is not easy.