a black swan is an unpredictable event that is beyond what is normally expected of a situation and has potentially severe consequences black swan events are characterized by their extreme rarity severe impact and the widespread insistence that they were obvious in hindsight 
one frequently cited example of a black swan event was the housing market crash of 2008 which led to the great recession other examples include the covid 19 pandemic the terrorist attacks of sept 11 and the hyperinflation crisis in zimbabwe investopedia michela buttignolunderstanding a black swanthe term was popularized by nassim nicholas taleb a finance professor writer and former wall street trader taleb wrote about the idea of a black swan event in a 2007 book prior to the events of the 2008 financial crisis taleb argued that because black swan events are impossible to predict due to their extreme rarity yet have catastrophic consequences it is important for people to always assume a black swan event is a possibility whatever it may be and to try to plan accordingly 1 some believe that diversification may offer some protection when a black swan event does occur taleb later used the 2008 financial crisis and the idea of black swan events to argue that if a broken system is allowed to fail it actually strengthens it against the catastrophe of future black swan events he also argued that conversely a system that is propped up and insulated from risk ultimately becomes more vulnerable to catastrophic loss in the face of rare unpredictable events 1taleb describes a black swan as an event that for extremely rare events taleb argues that the standard tools of probability and prediction such as the normal distribution do not apply since they depend on large population and past sample sizes that are never available for rare events by definition extrapolating using statistics based on observations of past events is not helpful for predicting black swans and might even make us more vulnerable to them the last key aspect of a black swan is that as a historically important event observers are keen to explain it after the fact and speculate as to how it could have been predicted such retrospective speculation however does not actually help to predict future black swans as these can be anything from a credit crisis to a war black swans and the housing market crashone of the most oft cited examples of a black swan event was the housing market crash of 2008 it occurred shortly after the 2007 publication of the black swan and it ticked all of the boxes in taleb s description prior to the crash it was impossible to calculate the probability that the housing market was in a bubble despite the serious economic consequences after the bubble popped many experts produced post facto rationalizations to explain why the collapse had been inevitable yet only a handful of economists and asset managers had seen it coming other examples of black swan eventsa black swan is any event that seems highly unlikely before it happens but in retrospect seems to have been nearly inevitable this definition is inherently subjective but these are some examples that are often cited as black swan events 