The lesson of the black swan is that we don't know how much we don't know.
For thousands of years, people thought that all swans were white. When someone discovered in Australia a rare black swan, he proved that the popular belief was wrong. (expectation - outlier)
Philosophers have used this story to illustrate the dangers of becoming too comfortable in what we think we know.
Examples of Black Swan events:
- World War 1
- Life of Jesus
- The Invention of Internet