Black swan theory

The Black swan theory, postulated by Nassim Nicholas Taleb, is used to describe the impact of events that come as a surprise in societal aspects. The event is unprecedented at a particular point in time until it happens.[1] The theory is a combination of mathematical and philosophical reasoning to explain and describe the randomness of uncertainty. The event generally has a major effect or is shocking in nature. This spurs interest from affected or concerned groups to make changes to current practices in order to promote positive events and avoid negative events. Black swan theory is closely related to beyond design basis accidents and are important in considering the long term safety of people living near power plants of various types.

The story behind the theory: In the 18th century, it was common western belief that all swans are white. This was based on all observations made of swans to date. In 1697, Willem de Vlamingh, a Dutch explorer discovered black swans in Australia. This came as a surprise, and resulted in profound changes in the scientific history of ecology and zoology.[1] Hence even though black swans exist, they are rare in nature.

The theory was developed to explain 3 major questions:

Question 1: Why do rare events effect history, science, finance and technology unreasonably?

  • Answer 1: They occur with low frequency, hence these events are not treated with high regard in realms where hypotheses are proven by highly frequent observations.

Question 2: Why are scientific methods insufficient at predicting these rare events?

  • Answer 2: Black swan events can only be effectively predicted and prepared for by mathematical and philosophical reasoning. Because scientific methods show that if events have a low frequency of occurrence they are disregarded.

Question 3: Why are people unaware of the sizeable role rare events play in history?

  • Answer 3: Low frequency events, unless catastrophic, are rarely given high priority in historical records.

The theory has three properties:

1) Rarity

  • The event is a surprise

2) Extreme impact

  • The event has major impact

3) Retrospective predictability

  • Looking back, the event could have been expected to take place

Example Rarity Extreme Impact Retrospective Predictability
Banqiao Dam, China 1975 1975 Flood with record rainfall of 189.5 mm per hour and 1060 mm per day, exceeding the average annual precipitation of about 800 mm [2] Dam failures resulted in roughly 171,000 deaths and 18 GW of power of loss [2] The accident could have been mitigated had original safety features been installed during initial construction of the dam.
British Petroleum Oil Spill, Gulf of Mexico 2010 An explosion at BP's Deep Water Horizon oil rig due to methane leakage resulted in a oil gusher which flowed for 87 days into the Gulf of Mexico [3] Largest accidental marine oil spill in history that resulted in 11 deaths and immeasurable environmental damage [3] The impact could have been minimized had BP repaired known defects on the rig such as cracking cement on the well.

For Further Reading


  1. 1.0 1.1 “Black Swan.” Internet:, [Apr. 04, 2014]
  2. 2.0 2.1 “Banqiao Dam.” Internet:, [Apr. 04, 2014].
  3. 3.0 3.1 “Deepwater Horizon Oil Spill.” Internet:, [Apr. 04, 2014].

Authors and Editors

Bethel Afework, Pria Roxanne Ghia, Robby Gunea, Ellen Lloyd, Kailyn Stenhouse, Jason Donev
Last updated: July 21, 2018
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