the.com/black swan

means An unpredictable, high-impact event that lies so far outside normal expectations that no one saw it coming — until it did, and then everyone insisted it was foreseeable.

from For centuries 'black swan' was Europe's go-to phrase for a flat impossibility — Latin writers used it, and the logic was airtight: all swans anyone had ever seen were white, so a black one simply couldn't exist. Then in the 17th century, Dutch explorers reached Australia and found swans that were, in fact, black — shattering a certainty built entirely on limited experience. The phrase lay around as a curiosity about faulty logic until the finance writer Nassim Nicholas Taleb repurposed it in the 2000s for rare, hard-to-predict events with outsized consequences, cementing the modern meaning.