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 paradox of thrift, in which the attempt to save more actually leads to the nation as a whole saving less, and the less-well-known paradox of flexibility, 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 – balanced budgets, a firm commitment to price stability – 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.
Paul Krugman, “Depressions are Different”, in Robert M. Solow, ed. Economics for the Curious: Inside the Minds of 12 Nobel Laureates. 2014.