John Maynard Keynes adopted the term herd psychology to explain the irrational behaviour of investors and banks in the boom leading to the ineevitable bust.
Keynes suggested the government should hire people to demolish South London and then rebuild it. He wasn’t serious, but he was making a serious point. If the government borrowed to create jobs, people would spend more, confidence would rise, and the economy would recover. If you picked the right moment, he insisted the extra spending would pay for itself by producing higher tax revenues.