Five whys
Definition
A root cause analysis technique developed by Sakichi Toyoda and used in the Toyota Production System, where the analyst asks 'why' in response to each answer until the root cause of a problem is identified — typically after five iterations.
Five whys is deceptively simple: ask why the problem occurred, take the answer, ask why that happened, and repeat until you've peeled back enough layers to reach a cause that can actually be changed. The 'five' is a heuristic, not a rule — some problems resolve in three iterations, others take seven.
Classic example:
- Why did the machine stop? The fuse blew.
- Why did the fuse blow? The bearing was overloaded.
- Why was the bearing overloaded? There was no lubricant.
- Why was there no lubricant? The lubrication pump failed.
- Why did the pump fail? The pump shaft was worn and hadn't been inspected.
Root cause: no preventive maintenance schedule for the pump. Fix the schedule, not the fuse.
On a whiteboard: The five whys is almost always done on a whiteboard or a large sticky note chain. Each 'why' becomes a new row, creating a visible chain from symptom to cause. Facilitators sometimes use the fishbone/Ishikawa diagram to structure multi-branch five whys sessions where there are multiple contributing causes.
Limitations: Five whys works best for simple linear cause chains. Complex systems with multiple interacting causes need more sophisticated tools — fault tree analysis, fishbone diagrams, or systems mapping. Five whys also risks 'why? because a person made a mistake' dead ends when the culture isn't blameless.
Snap the five whys chain from the whiteboard with BoardSnap and get a clean linear summary from symptom to root cause, with the action item at the bottom.
Examples
- A bug escapes to production: why? No automated tests. Why? Test writing wasn't part of the definition of done. Why? The team never defined done explicitly. Root cause: missing team norms.
- A sales rep loses a deal: why? Product lacked a key feature. Why? Feature was deprioritized. Why? No customer evidence supported it. Root cause: insufficient discovery process.
- An engineering team uses five whys on a whiteboard during a blameless postmortem, generating a chain that leads to a missing circuit breaker in the architecture.
- A coach teaches five whys to a junior PM team using a physical whiteboard and sticky notes, one row per iteration.
Snap a five whys. Ship its actions.
BoardSnap turns any whiteboard — including this one — into a summary and action plan.