Distinguish human error from system conditions

When a person is the proximate cause, ask why the system allowed the error to occur.

Why it works

The Five Whys is particularly important in systems with human operators because the proximate cause of most failures is a human action or omission. Stopping at "human error" as the root cause is almost always a failure of analysis: the deeper question is why the system’s design, training, culture, or conditions made that error likely. Toyota’s approach consistently reaches system-level causes rather than individual blame — not as a way of avoiding accountability, but because fixing the person does not fix the system that produced the error.

How to do it

1. When a "why?" answer names a person’s mistake, ask: "Why was the person able to make this mistake?" or "What conditions made this error likely?"
2. Look for: missing information, time pressure, absent safeguards, inadequate training, conflicting incentives.
3. Design the fix at the system level rather than targeting the individual.

Evidence

The distinction between proximate human error and systemic causes is a foundation of high-reliability organization (HRO) theory. Healthcare patient-safety research consistently finds that error reduction requires system redesign, not just individual retraining. The Institute of Medicine’s To Err Is Human landmark report grounded this at national scale, attributing tens of thousands of preventable deaths to system failures rather than individual incompetence and shifting patient-safety strategy toward system redesign. (observational)

Not all errors are systemic; some are genuine individual misjudgments that require individual-level responses. The skill is distinguishing the two, not assuming all errors are systemic.

Sources

• Reason (1990), Human Error — the Swiss cheese model and system conditions for error
• Reason, J. (2000). Human error: models and management. BMJ, 320(7237), 768–770.
• Kohn, L.T., Corrigan, J.M., & Donaldson, M.S. (Eds.) (2000). To Err Is Human: Building a Safer Health System. Institute of Medicine / National Academies Press, Washington, DC.

Common mistake

Using "it was human error" as the end of the analysis — which is the single most common way the Five Whys fails in organizations with blame-forward cultures.