The story behind the paradox of thrift goes like this. Suppose a large group of people decides to save more. You might think that this would necessarily mean a rise in national savings. But if falling consumption causes the economy to fall into a recession, incomes will fall, and so will savings, other things equal. This induced fall in savings can largely or completely offset the initial rise. Which way it goes depends on what happens to investment, since savings are always equal to investment. If the central bank can cut interest rates, investment and hence savings may rise. But if the central bank can’t cut rates — say, because they’re already zero — investment is likely to fall, not rise, because of lower capacity utilization. And this means that GDP and hence incomes have to fall so much that when people try to save more, the nation actually ends up saving less.