On 15 April 1788, early settlers in Australia found something they were not expecting and which, according to all common knowledge, could not possibly exist: yes, they found black swans which , says On This Day in The Daily Telegraph, were a "creature from ancient mythology". So rare were they that there was a belief that "all swans are white" and "black swan" had become a metaphor for something that could not exist. Now "black swan" has been adapted in Nassim Nicholas Taleb's theory to mean a large-impact, hard-to-predict, and rare event beyond the realm of normal expectations - such as the rise of the internet, the personal computer and World War I. (Thanks Wikipedia.) While others have dealt with the notion of improbability as it relates to its role in human history, Taleb suggests that "almost all consequential events in history come from the unexpected" and it is only in hindsight that we convince ourselves that these events are explainable.
Another piece of information gleaned from reading about this, John Stuart Mill, who first used the Black Swan narrative to discuss falsification, was greatly influenced in his studies by his wife, and then daughter, who were instrumental in his work in human (and women's) rights. He and his wife, who was already married when the met, shared what Wikipedia described as a close but chaste friendship for 21 years - before her first husband died and she and Mill married.