metaphor that describes an event that comes as a surprise, has a major effect, and is often inappropriately rationalized after the fact with the benefit of hindsight. The term is based on an ancient saying which presumed black swans did not exist, but the saying was rewritten after black swans were discovered in the wild.
The theory was developed by Nassim Nicholas Taleb to explain:
The disproportionate role of high-profile, hard-to-predict, and rare events that are beyond the realm of normal expectations in history, science, finance, and technology.
The non-computability of the probability of the consequential rare events using scientific methods (owing to the very nature of small probabilities).
The psychological biases which blind people, both individually and collectively, to uncertainty and to a rare event's massive role in historical affairs.
Examples: The Internet, The dissolution of the Soviet Union. The internet has had globally disrupting ripples of effect which are ever impacting in the present and in the future including; blockchains, taxing robots, social costs (negative externalities).