So the story of the baby-sitting co-op is not a mere amusement. If people would only take it seriously—if they could only understand that when great … - Paul Krugman

When the economy is in a depression, scarcity ceases to rule. Productive resources sit idle, so that it is possible to have more of some things without having less of others; free lunches are all around. As a result, all the usual rules of economics are stood on their head; we enter a looking-glass world in which virtue is vice and prudence is folly. Thrift hurts our future prospects; sound money makes us poorer. Moreover, that's the kind of world we have been living in for the past several years, which means that it is a kind of world that students should understand. […] Depression economics is marked by paradoxes, in which seemingly virtuous actions have perverse, harmful effects. Two paradoxes in particular stand out: the , in which the attempt to save more actually leads to the nation as a whole saving less, and the less-well-known , in which the willingness of workers to protect their jobs by accepting lower wages actually reduces total employment. […] In times of depression, the rules are different. Conventionally sound policy—s, a firm commitment to —helps to keep the economy depressed. Once again, this is not normal. Most of the time we are not in a depression. But sometimes we are—and 2013, when this chapter was written, was one of those times.

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.

On the whole, the monetarism for which Friedman first became famous seems clever, brilliantly argued, but shallow ― and perhaps even a bit disingenuous. Friedman's writings from that period have the feel of a smart man who knows what he wants to believe looking hard for supporting arguments. And I think it is fair to say that up until the late 1960s Friedman and his followers, while influential, were regarded by many of their colleagues as faintly disreputable.