Europeans once thought all swans were white. “White” was part of how they defined “swan.” Then black swans were discovered, and the definition changed forever.

In his 2007 book The Black Swan, Nassim Nicholas Taleb says the Black Swans of his title can appear at any time, in the form of financial crises, wars, and other unexpected events that have profound, irreversible consequences. Taleb draws on philosophy, mathematics, economics, and other disciplines to explain in plain English why we seldom prepare for these events adequately. The way our brains process knowledge, combined with the conventions of statistical modeling, lull us into believing the future will resemble the past.

The Black Swan was published shortly before the financial crisis of 2008, and that particular Black Swan event helped Taleb’s ideas reach a broad, popular audience. The book, which has been translated into more than 30 languages, also sparked debates in several academic disciplines that continue to this day.