A Black Swan is rare, extreme, and only explainable in hindsight

Taleb defines a Black Swan event by three features: it lies outside the range of normal expectations, it carries an extreme impact, and — crucially — human nature makes us concoct explanations for it after it happens that make it look like it should have been predictable all along. The name comes from Europeans who, having only ever seen white swans, considered the black swan a logical impossibility until one was discovered in Australia.

The events that actually redirect history — major wars, market crashes, the rise of a disruptive technology — routinely fit this profile: essentially unthinkable before they happen, and treated as obvious in retrospect afterward. This retrospective obviousness is itself a trap, because it convinces people they're better forecasters than they actually are.

The core warning: don't judge your predictive ability by how well you can explain the past — that's nearly free. Judge it by what you can actually see coming, which is far less than we assume. Takeaway: hindsight clarity is not foresight.