Europeans once thought all swans were white, and white was part of how they defined 'swan.' Then black swans were discovered, and the definition changed forever. In his 2007 book, 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. He draws on philosophy, mathematics and economics to explain 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. We must beware of, and be prepared for, the unexpected.