Before the discovery of Australia people in the old world were convinced that all swans were white. The sightings of black swans in Australia are an example of the limitations of our knowledge. Taleb uses this metaphor for events that are rare, have extreme impact and are predictable only in retrospect. As Taleb says: “Go through you own existence. Count the significant events, the technological changes, and the inventions that have taken place in our environment since since you were born and compare them to what was expected before their advent. How many of them came on schedule? Look into your own personal life, to your choices of profession, say, or a meeting with your mate, your exile from your country of origin, the betrayals you faced, your sudden enrichment or impoverishment. How often do these things happen according to plan?” He argues that almost all discoveries, inventions and events have been black swans, and not the result of top down planning.