Human factors: understanding why competent people make mistakes

Why does an experienced pilot, a renowned surgeon or a seasoned manager sometimes make a mistake that looks obvious in hindsight? Human factors offer an answer: error is not primarily a matter of competence, but of attention, fatigue, communication and organisation. Here are the essential concepts.

What are human factors?

Human factors covers everything that influences the performance of an individual or a team: attention, memory, fatigue, stress, cognitive biases, communication, work organisation, environment. The discipline developed in aviation and industry before being widely adopted in healthcare.

Its founding principle: human beings are not infallible machines. Rather than demanding perfection, we need to understand their limits and design systems that take them into account.

An error is not misconduct

An error is an action that fails to achieve the intended result, without any intention to do harm. Treating it as individual misconduct has a perverse effect: it encourages people to hide errors and prevents anyone from learning from them. The safest organisations instead develop a “just culture”, where errors can be reported so their causes can be understood, while people remain accountable for their actions.

The Swiss cheese model

British psychologist James Reason proposed an image that has become famous: each layer of protection in an organisation (procedures, supervision, training, individual vigilance) is like a slice of cheese full of holes. An incident occurs when the holes in several slices line up.

The Dirty Dozen: 12 classic traps

Developed in the early 1990s by Gordon Dupont for Transport Canada, in the field of aircraft maintenance, the “Dirty Dozen” lists twelve frequent causes of human error:

• lack of communication;
• complacency (“we’ve always done it this way”);
• lack of knowledge;
• distraction;
• lack of teamwork;
• fatigue;
• lack of resources;
• pressure;
• lack of assertiveness;
• stress;
• lack of awareness;
• norms (tolerated “shortcuts” that become the rule).

Each trap has a countermeasure: read-back, systematic checks, checklists, status updates, the right to raise an alert…

Situational awareness

Mica Endsley described situational awareness in three levels: perceiving the important elements, understanding what they mean, and anticipating how they will evolve. Many errors can be explained by a failure at one of these levels: the information was not seen, was misinterpreted, or its consequences were not anticipated. In a team, the challenge is to share the same picture of the situation.

Stress, fatigue and workload

Beyond a certain threshold, stress degrades performance: attention narrows into tunnel vision. Fatigue impairs alertness, often without the person noticing. Both are among the non-technical skills that safety-critical industries recommend training.

What can you do in practice?

• Train teams in human factors through immersive simulations rather than theory alone.
• Introduce simple tools: briefings, checklists, read-back, status updates.
• Encourage everyone to speak up, whatever their position in the hierarchy.
• Analyse incidents without looking for a culprit, so the whole team can learn.

Sources

• Reason J., “Human error: models and management”, BMJ, 2000
• Endsley M. R., “Toward a theory of situation awareness in dynamic systems”, Human Factors, 1995
• French National Authority for Health (HAS) — Human factors competency framework, 2026 (in French)

Further reading

• Crew Resource Management: what aviation teaches teams
• Debriefing: the key to learning from experience
• Our method