Politicians who preside over economic booms often develop delusions of competence. You can see this domestically: Jeb Bush imagines that he knows the secrets of economic growth because he happened to be governor when Florida was experiencing a giant housing bubble, and he had the good luck to leave office just before it burst. We’ve seen it in many countries: I still remember the omniscience and omnipotence ascribed to Japanese bureaucrats in the 1980s, before the long stagnation set in.

This is the context in which you need to understand the strange goings-on in China’s stock market. In and of itself, the price of Chinese equities shouldn’t matter all that much. But the authorities have chosen to put their credibility on the line by trying to control that market — and are in the process of demonstrating that, China’s remarkable success over the past 25 years notwithstanding, the nation’s rulers have no idea what they’re doing.

Start with the fundamentals. China is at the end of an era — the era of superfast growth, made possible in large part by a vast migration of underemployed peasants from the countryside to coastal cities. This reserve of surplus labor is now dwindling, which means that growth must slow.

But China’s economic structure is built around the presumption of very rapid growth. Enterprises, many of them state-owned, hoard their earnings rather than return them to the public, which has stunted family incomes; at the same time, individual savings are high, in part because the social safety net is weak, so families accumulate cash just in case. As a result, Chinese spending is lopsided, with very high rates of investment but a very low share of consumer demand in gross domestic product.