There are many economic puzzles, but there are only two really great mysteries. One of these mysteries is why economic growth takes places at differe… - Paul Krugman

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There are many economic puzzles, but there are only two really great mysteries.
One of these mysteries is why economic growth takes places at different rates over time and across countries. Nobody really knows why the U.S. economy could generate 3 percent annual productivity growth before 1973 but only 1 percent afterward, nobody really knows why Japan surged from defeat to global economic power after World War II, while Britain slid slowly into third-rate status. At any given time there are always policy entrepreneurs willing to claim that they have all the answers, but we'll come to that story in later chapters.
The other mystery is the reason why there is a business cycle ― the irregular rhythm of recessions and recoveries that prevents economic growth from being a smooth trend. It was in challenging the orthodox, Keynesian view of business cycles that conservatives first forced a major rethinking of economics.