The Black Swan

The Black Swan: The Impact of the Highly Improbable is a 2007 book by Nassim Nicholas Taleb, a former options trader. It focuses on the outsized impact of rare, unpredictable events and on the human tendency to build simplistic explanations for them after the fact. Taleb calls this the Black Swan theory. The book is part of his five-volume Incerto series, which also includes Fooled by Randomness (2001), The Bed of Procrustes (2010-2016), Antifragile (2012) and Skin in the Game (2018).

The book mixes reflections on knowledge, aesthetics and ways of living, using fiction and anecdotes from the author's life to develop its ideas. It moves from literary subjects at the beginning to scientific and mathematical ones later on. The first part and the start of the second deal with psychology; the latter half of the second part and the third address science and business; the fourth offers advice on living with uncertainty and still enjoying life. Taleb describes it as an essay or narrative built around a single idea: our blindness to randomness, particularly to large deviations.

His central argument is that trying to predict Black Swans is futile; the aim should be to build robustness against negative shocks and the capacity to benefit from positive ones. Banks and trading firms, he argues, are vulnerable to such events, and their financial models leave out losses they should anticipate. Whether an event is a Black Swan depends on the observer: what is a surprise to the turkey is no surprise to the butcher. The advice is to avoid being the turkey by finding one's vulnerabilities, so that the Black Swans can be turned white.

Taleb distinguishes between Mediocristan, where values cluster around an average and extremes barely shift it, as with human height, and Extremistan, where a few extreme cases dominate the total, as with wealth. In Extremistan, Gaussian distributions are a poor guide. He also criticises epistemic arrogance, the habit of believing we know more than we do, and recommends the barbell strategy: keeping most of one's money in very safe instruments and a small portion in highly speculative bets.

The term has a long history. Its earliest known use is in Juvenal, who compared a good person to a black swan, and it became a common London expression in the sixteenth century for something impossible, since every known swan was white. Aristotle used swans in his syllogisms, and Hume drew on the example to question induction. The discovery of black swans in Australia showed that accumulated experience cannot guarantee universal truths.

The book was a major success. It spent 36 weeks on the New York Times bestseller list, was published in around thirty languages, and has been described as one of the most influential books since the Second World War. It also drew criticism. Mathematician David Aldous judged Taleb sensible on financial markets but prone to irrelevance or exaggeration elsewhere, and Taleb replied to his critics by pointing to logical errors in their arguments.