Black swan

Mankind were wrong, it seems, in concluding that all swans were white: are we also wrong, when we conclude that all men's heads grow above their shoulders, and never below, in spite of the conflicting testimony of the naturalist Pliny? As there were black swans, though civilised people had existed for three thousand years on the earth without meeting with them, may there not also be "men whose heads do grow beneath their shoulders," notwithstanding a rather less perfect unanimity of negative testimony from all observers? Most persons would answer No; it was more credible that a bird should vary in its colour, than that man should vary in the relative position of his principal organs.

If you tell me that there is or that there is not a black swan or a white raven, I want to know where you mean; and that you can only show me,—no description will answer the purpose.

The original propounder of 'all swans are white' presumably based it on a sample of hundreds or thousands; but the verifications before the Australian black swan was discovered must have run into millions

This concept of "observation" is not like that of seeing a black swan, to mention a famous classical example. New particles leave signatures in the detector that on an event by event basis cannot be distinguished by other processes (background).

I do but ſpeake in the perſon of Demetrius, & vnder Hippolita ſhadovv vvhat I intend to the rare, and neuer enough vvondred at Moſpa, the black ſvvan of beauty, & madg-hovvled of admiration.

A Virgin too, untouch'd, and chaſte, / VVhom Man ne'er took about the VVaiſte. / She's a rare Bird! find her vvho can, / And much reſembling a black Svvan.

A small number of Black Swans explain almost everything in our world, from the success of ideas and religions, to the dynamics of historical events, to elements of our own personal lives. […] Fads, epidemics, fashion, ideas, the emergence of art genres and schools. All follow these Black Swan dynamics.

The details of this catastrophe [the 2011 Fukushima nuclear accident] were unforeseeable, leading some to conclude this was a black swan event – something so wildly unexpected, so enormous in its impact, that it seems to defy our understanding and expose the fragility of our knowledge of the world. How could anyone have predicted this? […] In the face of black swans – also known as fat-tail events, for the way their occurrences are distributed along a probability curve – market pricing may be impossible.

Worried that Greece could go belly up? So-called black swan funds – named for rare and unexpected events – offer a way to profit in the event of a market collapse.