Black Swan theory says things happen that were previously thought to be impossible or never thought of at all. The idea was popularized by Naseem Taleb in his best selling books, fooled by randomness and the black swan. People could only imagine white swans because all swans ever seen had possessed white feathers. In the 17th century, London, it was common to refer to impossible things as black swans. But when the but then the Dutch explorer, William de Vlamen, sorry, people of Holland went to Western Australia he saw a black swan suddenly. He said: "The unthinkable and unthought was real"