The Black Swan Events theory was introduced by Nassim Nicholas Taleb in 2007. A Black Swan event is an event in human history that was not considered possible at the time it occurred. After subsequent analysis, it can usually be concluded that it should have been predictable.
The term originates from the (Western) belief that all swans were white until, in 1697 the Dutch explorer Willem de Vlamingh discovered black swans on the Swan River in what is now Perth, Western Australia.
Taleb’s theory concentrates on unexpected events of large magnitude and consequence and their dominant role in history. Such events, considered extreme outliers, collectively play vastly larger roles than regular occurrences