Financial markets accommodate both prudent insurers and reckless gamblers. They provide investors with an opportunity to diversify their portfolios, and allow gamblers to bet on future movements in interest rates. The coexistence of the two can allow speculators to make profits by stabilising prices—buying when markets are fearful, and selling when they are greedy. But when the gambling motive overwhelms the insurance motive, speculation becomes destabilising and then risk, far from being minimised by careful management, becomes concentrated in the hands of those who understand least what they are doing. And when regulators perceive insurance when they should see wagering, their actions magnify a crisis rather than minimise it. Such destabilising speculation, mischaracterised by regulatory authorities as prudent risk assessment, is what caused the global financial crisis of 2008. ... The coexistence of insurance and gambling goes back to the earliest days of markets in risk, and the interaction of the two has been central to financial history. But it was four developments in the second half of the 17th century that combined to frame the way we think about risk, and the institutions we have for dealing with it, through to the present day.