A black swan event is the idea that things that were never imagined do come to pass. The idea was recently popularized by Nassim Taleb1. The concept dates to the seventeenth century when “Black” swans were thought of as impossible events (since all known swans were white). However, Dutch explorer Willem de Vlamingh went to western Australia in 1697 and discovered a black swan. Illustrating that the unimaginable can come to pass2. Black swans are unknown unknowns.
1. Taleb, N. N. Fooled by Randomness: The Hidden Role of Chance in Life and in the Markets. (Random House, New York, 2008).
2. Voss, C. & Raz, T. Never Split the Difference: Negotiating As If Your Life Depended On It. (Harper Business, New York, 2016).