Know about the paradox of thrift, popularized by John Maynard Keynes

60-Second Adventures in Economics. Number Two, The Paradox of Thrift. Much like a child getting his pocket money, one of the biggest economic questions is still whether it's better to save or spend. Free marketeers, like Hayek and Milton Friedman, say that even in difficult times, it's best to be thrifty and save. Banks then channel the savings into investment in new plants, skills, and techniques that let us produce more. And even if this new technology destroys jobs, wages will drop, and businesses hire more people, so unemployment falls again. Simple, at least in the long run.

But then a live fast, die young kind of chap called John Maynard Keynes cheerfully pointed out that in the long run, we're all dead. So to avoid the misery of unemployment, the government should instead spend money to create jobs, whereas if the government tighten its belt when people and businesses are doing the same, less is spent, so unemployment gets even worse. That is the paradox of thrift. So instead, they should spend now and tax later when everyone's happy to pay, though making people happy to pay tax was something even Keynes didn't solve.