https://www.theguardian.com/business/2020/mar/31/coronavirus-should-not-have-caught-leaders-and-markets-off-guard Events like the Covid-19 pandemic, the US housing-market crash of 2007-09 and the terrorist attacks of 11 September 2001, are often called “black swans”. The term is meant to suggest that no one could have seen them coming.
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