The black swan theory or theory of black swan events is a 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 that blind people, both individually and collectively, to uncertainty and to a rare event’s massive role in historical affairs.Unlike the earlier and broader “black swan problem” in philosophy (i.e. the problem of induction), Taleb’s “black swan theory” refers only to 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.
More technically, in the scientific monograph ‘Silent Risk’, Taleb mathematically defines the black swan problem as “stemming from the use of degenerate metaprobability”