Low-Probability High-Impact (The Black Swan)

In autumn I will be hosting a dinner event at Rhubaba in Edinburgh. I'm here right now for the festival, and so me and the directors are going to have a meeting tonight and talk about what's going to happen at the dinner event.

I thought I'd try and get it all clear in my head before then.


A while back a friend told me about a traumatic event that happened to him when he was young. He was in the high street of the town where he lived, in the middle of the afternoon, when a man attacked him with a knife and stabbed him in the back 17 times. By chance, none of his internal organs had been damaged by the attack and my friend survived. The attacker was a man with severe mental health problems who had escaped from a secure facility in the midst of a psychotic episode. He handed himself in to a police station later in the afternoon.

My friend went on to speak about some counselling or therapy he had received. As I understood it at the time, the therapist was a specialist in the psychological trauma caused by low-probability, high-impact events such as the random violent attack my friend had experienced. Other such events included being struck by lightning, surviving a plane crash or winning the lottery.

Part of the problem, according to his therapist, is that experiencing such unlikely events skews our already limited understanding of probability. I'd read about the human mind's limitations when it came to probability, for example, the fear of hypothetical terrorist attacks far outweighs the fear of being hit by a car, despite the mathematical probabilities of being affected by either event.

According to the therapist, the stress caused by experiencing such an unlikely event could manifest itself in several ways; you might believe that you were unlucky and that more of these unlikely events could happen to you, or you might believe that you were now invincible because you had survived something that very few people have ever experienced. Both of these ideas are a kind of psychosis - a misunderstanding of the real probability of events, but then our everyday understanding of probability is already psychotic in that sense.

I was fascinated by the idea that such different events as winning the lottery or surviving a plane crash were united by the psychological trauma that they could cause. And I was particularly fascinated by the interplay of abstract and empirical understanding. Experiencing a low-probability event gave the human mind an empirical insight into a reality where such things were possible, and yet the mind did not have the capacity to successfully abstract that knowledge into a rational understanding of probability.


When Rhubaba asked me to host a dinner event, I decided that I'd ask my friend to attend, along with some other people who had experienced low-probability, high-impact events. I would also ask a psychologist, or maybe a specialist counsellor of the sort my friend had spoken about, and maybe a mathematician who could speak about probability.

I spoke to my friend again, and it turned out that I'd got some of the details a bit wrong: the counselling wasn't specific to the kind of low-probability event that he had experienced, and the anxiety could be described as a form of Post Traumatic Stress which can be caused by many different kinds of events, not just unlikely ones. Also, my friend couldn't remember the term used by a psychiatrist to describe low probability events. The term I have been using - "low-probability high-impact" - is a bit unwieldy, so I'm trying to find something better.

Sian, one of Rhubaba's directors, suggested the term "Black Swan", taken from the book The Black Swan by Nassim Nicholas Taleb.

A Black Swan event, according the wikipedia page, can be identified in three ways:

"1. The event is a surprise [...].
2. The event has a major effect.
3. [The event] is rationalized by hindsight [...]"

Taleb's writing is more concerned with economics and history - large scale, unpredictable events like the recent global recession, or the fall of Communism. Things that define the way the world is now, but that we could never have predicted. We rationalise them in retrospect - claiming them to be articulable in terms of cause and effect, but Taleb believes that their essence is in their unpredictability.

Although he is writing about things of a very different scale, the events I have been thinking about are similar in quality, and the post-rationalisation process is linked to the Post Traumatic Stress response. The inability of the human mind to adequately comprehend low-probability events causes a pathological rationalisation of the experience of such events.


So, although we have lots of work to do, maybe we have a title for the event. The Black Swan Dinner.