The Black Swan Theory by Nassim Taleb

The Black Swan Theory refers to a large-impact, hard-to-predict, and rare event beyond the realm of normal expectations. The term black swan comes from the accepted idea for thousands of years that all swans were white. A black swan had never been seen so it was accepted that they did not exist. But when a black swan was discovered in Perth, Western Australia, it completely challenged existing thought and so the “black swan” became a metaphor for when something unthinkable, unexpected and unpredictable occurs.