# Black swan A Black Swan is an event that is surprising (to the observer), has major effect, and, after being observed, is rationalized in hindsight. The theory of black swans is epistemological, relating to the limited knowledge and understanding of the observed events. The term was popularized by [[Nassim Nicholas Taleb]] in the book [[The Black Swan (book)]]. It has been associated with concepts such as heavy tails, non-linear payoffs, model error and even Knightian uncertainty. ## Related - [[Dragon King (DK)]]