Until the seventeenth century, people could only imagine white swans because all swans ever seen had possessed white feathers. In seventeenth-century London it was common to refer to impossible things as “Black Swans.” But then the Dutch explorer Willem de Vlamingh went to western Australia in 1697—and saw a black swan. Suddenly the unthinkable and unthought was real. People had always predicted that the next swan they saw would be white, but the discovery of black swans shattered this worldview.
