As then, this causes people to seek safety in ways which in fact increase risk, for them individually and for societies collectively. The flames of this epidemiological fire are increasingly being fanned by social media. The most visible manifestation of these failures occurs at times of financial crisis, such as during a bank run. These are contagious losses of trust. While it may seem individually rational to run, bank runs can be collectively calamitous for societies as a whole, as during the global financial crisis and MMR episodes. As in those episodes, contagion is often spread by social as well as financial channels. “Popular narratives” emerge in crisis that propagate panic, tipping economies into recession. 35  Robert Shiller has recently shown how past recessions and depressions have often generated pessimistic popular narratives about the economy or financial system. 36  Economic expectations, like measles, can  follow epidemiological dynamics as pessimism spreads contagiously. This tipping point in expectations provides a plausible account of the cliff-edge fall in GDP at the time of the Great Recession, the Great Depression and several episodes in between. These epidemics in expectations can be potent even during tranquil times. Sociologists have shown that individuals’ everyday decisions are often shaped by friends’ and associates’ views and behaviours, irrespective of fundamental factors. It is not just extreme optimism and pessimism, exuberance and depression, fear and hubris that are contagious. So too are dieting, exercise and gym membership. 37  That appears to be true of financial market dynamics too.

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