The price of bitcoin, the world’s most popular cryptocurrency, fell by almost 20% at the weekend, from around $57,000 on December 3rd to $45,000 the next day (it has since partially recovered, to around $49,000). Other popular coins, including Ethereum, shed a similar proportion of their value. The market capitalisation of all crypto assets fell by $400bn to $2trn, before picking up slightly. Why did prices fall again?