# Normalisation of Deviance (Challenger)

*Tom Geraghty · Stories & Cases, Safety & Human Error*

Explores Diane Vaughan's 'normalisation of deviance' (coined in The Challenger Launch Decision): the gradual process by which unacceptable practice becomes accepted as normal, as deviance repeated without catastrophic results becomes the social norm. It isn't about rule-breaking per se, nor intent to cause harm; it's the slow, interpersonally 'acceptable' drift from a safe condition toward greater risk, in a long incubation period before disaster. Every skipped checklist or silenced alarm makes the next one easier because it was fine last time. At NASA, a strong cultural faith in O-ring redundancy turned 'a no-go below 53°F' into 'lower temperatures are in the direction of badness' — and the same pattern recurred with Columbia's foam strikes 22 years later. Vaughan identifies production pressure, scarcity, competition for funds and structural secrecy as drivers, alongside a lack of psychological safety where those who notice the drift don't speak up. The piece extends the concept to the Costa Concordia (the captain's normalised off-route 'salute', promoted by Carnival as marketing) and the Boeing 737 MAX (MCAS issues known since 2016 but not urgent because nothing bad had yet happened). Feynman's image captures it: pulling the trigger in Russian roulette, the gun doesn't go off, so it must be safe to pull again — except we don't even know how many bullets are in the gun. Detecting and correcting the drift takes effort, reflection, and psychological safety; Vaughan notes it's easier to prevent than to correct.

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## Connected concepts (18)

- [Calculus of Voice](https://explore.psychsafety.com/n/the-calculus-of-voice.md)
- [The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA](https://explore.psychsafety.com/n/vaughan-1996.md) (paper)
- [Crew Resource Mgmt](https://explore.psychsafety.com/n/crew-resource-management-and-psychological-safety.md)
- [Local Rationality](https://explore.psychsafety.com/n/local-rationality.md)
- [The Vasa Disaster](https://explore.psychsafety.com/n/the-vasa-disaster.md)
- [Blametropism](https://explore.psychsafety.com/n/blametropism.md)
- [Groupthink: Psychological Studies of Policy Decisions and Fiascos](https://explore.psychsafety.com/n/janis-1982.md) (paper)
- [Learning from Error](https://explore.psychsafety.com/n/learning-from-error-or-punishing-it.md)
- [Lessons from Everest: The Interaction of Cognitive Bias, Psychological Safety, and System Complexity](https://explore.psychsafety.com/n/roberto-2002.md) (paper)
- [The Cost of Silence: Normalization of Deviance and Groupthink](https://explore.psychsafety.com/n/nasa-normalization-deviance-2014.md) (paper)
- [The Dark Side of Organizations: Mistake, Misconduct, and Disaster](https://explore.psychsafety.com/n/vaughan-1999.md) (paper)
- [Watermelon Effect](https://explore.psychsafety.com/n/the-watermelon-effect-and-greenwashing.md)
- [Chernobyl](https://explore.psychsafety.com/n/chernobyl.md)
- [Everest & PS](https://explore.psychsafety.com/n/everest.md)
- [Normal Accidents](https://explore.psychsafety.com/n/normal-accidents.md)
- [Psychological Safety Books](https://explore.psychsafety.com/n/psychological-safety-books.md)
- [Guardrails & Failure](https://explore.psychsafety.com/n/psychological-safety-84-guardrails-and-failure.md)
- [Zero Defects & PS](https://explore.psychsafety.com/n/psychological-safety-89-zero-defects.md)