Most post-mortems of the financial crisis have diagnosed one of two causes of near-death: greed or stupidity. The greed school focuses on the excess of the world’s financiers and the spendthrift ways of American consumers and home-buyers. The stupidity camp zeroes in on the mistakes of individuals and institutions: the CEOs who did not understand their own off-balance sheet assets; the ratings agencies who believed sub-prime mortgages could be packaged into triple A securities; the regulators who missed Bernard Madoff’s fraud.

Both arguments are right. But individual ignorance and avarice are just sideshows; the biggest driver of the crisis was systemic. The boom – and bust – happened because investors obeyed the logic of financial markets.