CockroachDB Glossary

Black Swan Event

A black swan event is an event that has the following three attributes:

  1. It was unexpected.

  2. It had significant, wide-ranging consequences.

  3. After it happens, people will suggest that it was predictable, despite the fact that it was not widely predicted before it happened.

This definition comes from mathematical statistician Nassim Taleb, who coined and popularized the term in his books Fooled by Randomness and The Black Swan.

However, in everyday language when people talk about a “black swan event,” they’re generally thinking just about unexpected events with wide-ranging consequences. The third criteria – that people will rationalize the event as predictable after the fact – isn’t typically discussed.

Officially the term doesn’t have a positive or negative connotation. Black swan events can theoretically be good or bad or neutral. In the real world, however, the term is often used to describe events with negative impacts, such as financial crashes, widespread service outages, and even natural disasters and terrorism.

Long story short: while the official definition of a black swan event is quite a bit more nuanced, in everyday life the term is often used to mean something pretty simple: an unexpected event with significant negative consequences.

(The name, in case you’re wondering, comes from the once-widespread perception that all swans were white, and black swans either didn’t exist or were incredibly rare. In reality, black swans do exist. But they’re only native to Australia, so they’re quite rare everywhere else – including in Europe, where the idea of a “black swan” as a symbol for something unpredictable, unexpected, or unlikely first came to be used.)

Black swan events in technology

In the tech industry, most discussion of black swan events is typically related to infrastructure, and infrastructure failures leading to service outages.

On a global scale, a black swan event in technology could be something like a coronal mass ejection from the sun causing a kind of natural EMP that knocks out electronic systems over a large area. (Whether this would be a true black swan event is debatable, considering that it has happened before, but it happens only rarely and is considered unlikely).

More commonly, though, discussions of black swan events in technology are company-specific, meaning that a “black swan event” is an event that significantly and negatively impacts the company’s services, generally due to some kind of infrastructure failure or outage.

Examples of potential company-level black swan events in technology include:

* Cloud provider outages.

* Power outages.

* System failures.

* Human mistakes.

Real-world example of a black swan event in tech

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