Black Swan & Gray Rhino
Professor Nassim Nicholas Taleb of New York University issued a book concerning Black Swan in 2007, and Professor Michele Wucker of Columbia University publicized her theory in 2013 concerning Gray Rhino. Thus these two terms are widely used, firstly in the financial market, but later in every aspect.
Black Swan denotes the chance of happening is extremely slight or even impossible, but it really happened. Like the Circuit Breaker of Mar 2020, the US market was in a sound rising trend over a decade, and even one month ago broke record high, but avalanche came suddenly.
Gray Rhino is a disastrous happening of large scale, the chance of happening is quite high or impossible to avoid, but underestimated. Such as the Lehman Brothers incident of 2008 was neglected because just a few months ago, the Bear Stearns was saved and people would not believe the 10 greatest commercial banks united together and the White House would not save the Brothers.