Black Swan
An extreme, unpredictable, high-impact event that falls outside the range of normal expectations and is rationalised as predictable only in hindsight.
Coined by Nassim Taleb, a Black Swan is an event that is (1) an outlier — outside regular expectations, (2) carries extreme impact, and (3) is explained as predictable only after the fact. For traders, examples include the 2008 financial crisis, the March 2020 COVID crash, and the 1987 single-day 22% market drop.
The key insight is not to predict Black Swans — they are by definition unpredictable — but to build portfolios and risk structures that can survive them: keep position sizes small, hold cash, consider tail hedges, and never use leverage that a single bad day can wipe out.
Related Terms
Capital Preservation
The principle of protecting trading capital above all else — because you cannot trade without capital, survival is the first objective.
BeginnerConditional Value at Risk (CVaR)
The average loss in the worst-case tail beyond the VaR threshold; it answers how bad losses are when VaR is breached, not just how often.
AdvancedHedging
Opening an offsetting position to reduce the net risk of an existing trade or portfolio against adverse price movements.
IntermediateRisk of Ruin
The statistical probability that a trader will lose enough capital to be forced out of trading entirely, given their edge and risk per trade.
AdvancedSystematic Risk
Risk that affects the entire market or a broad asset class and cannot be eliminated through diversification.
IntermediateTail Risk
The risk of rare, extreme outcomes in the far ends of a return distribution — events that standard models greatly underestimate.
AdvancedValue at Risk (VaR)
The maximum loss not expected to be exceeded over a given time horizon at a chosen confidence level, e.g. 95% or 99%.
Advanced