In 1991, the Nobel laureate economist Paul Krugman, who is perhaps the world’s leading Keynesian today, showed that whether or not expectations are self-fulfilling depends on underlying economic conditions. If an economy’s fundamentals are very weak, a crisis will inevitably occur sooner or later; if its fundamentals are very strong, a crisis never happens; and if they are in an intermediate range, a crisis happens if – and only if – people expect one.