Root Cause Analysis
Root Cause Analysis, most commonly run as the Five Whys, means asking why a problem happened repeatedly until you hit a systemic cause you can actually fix, instead of stopping at the first answer that blames a person.
Six numbered boxes run in two rows, an arrow carrying you rightward from one why to the next until the chain wraps and lands on something systemic.
Reach for this when…
- The same defect or complaint keeps recurring despite fixes being applied each time.
- A postmortem stops at 'human error' and everyone accepts it and moves on.
- You need to justify a more expensive upfront fix by showing what the recurring cost actually is.
How to run it
- State the problem precisely, with the specific instance, not the general pattern.
- Ask why it happened, and answer with fact, not assumption.
- Ask why again to that answer, and keep going.
- Stop when you reach a cause that's systemic - a process, a check, a design - not a person.
- Fix the system-level cause, and check the earlier stopping points weren't also worth fixing.
A worked example
Situation. Andrei Popescu managed quality at Somes Aqua, a shrimp processing plant in Cluj, Romania, where export inspectors kept rejecting batches and each rejection got written up as worker carelessness.
Applied. He ran the Five Whys on the last three rejected batches and traced the chain past the workers entirely, landing on a cold-chain sensor that hadn't been recalibrated on schedule for months.
Result. The calibration schedule got fixed, rejections dropped sharply, and the plant stopped disciplining staff for a fault that was never theirs to begin with.
The catch
Five Whys works best on a single, well-defined incident - run it on a vague, multi-cause problem and it produces a confident-sounding chain that's really just one person's theory. It also tends to stop wherever the asker's authority or comfort runs out, which is exactly where the real cause often lives.
If the fifth why lands on a person's name, you likely stopped one why too early.
Origin: Sakichi Toyoda / Toyota Production System