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What is 5 Whys

Also known as: five whys, 5 whys technique, 5 whys example, five whys method

Definition

5 Whys is a way to find the root cause of a problem: you ask why it happened, then why again, usually about five times, until you reach a cause you can fix.

Why it matters

Most businesses fix symptoms rather than root causes, so the same problems keep coming back.

Common mistakes

Stopping after the first why, which usually results in blaming an employee rather than fixing the system.

Related terms

Worked example

Taiichi Ohno's five whys: why did the machine stop?

Ohno's own example of the method, from a machine on the shop floor.

  1. Why 1

    Why did the machine stop? There was an overload, and the fuse blew.

  2. Why 2

    Why was there an overload? The bearing was not lubricated enough.

  3. Why 3

    Why was it not lubricated enough? The lubrication pump was not pumping enough.

  4. Why 4

    Why was it not pumping enough? The shaft of the pump was worn and rattling.

  5. Why 5

    Why was the shaft worn? There was no strainer, so metal scrap got in.

The fix was to install a strainer. Replacing the fuse would have answered only the first why, and the machine would have stopped again.

Source: Taiichi Ohno, Toyota Production System: Beyond Large-Scale Production, 1988

Fix at which why?

The machine stopped. Overload, the fuse blew. Bearing not lubricated enough. Pump not pumping enough. Pump shaft worn. No strainer, scrap got in.⁨The machine stopped⁩⁨Overload, the fuse blew⁩⁨Bearing not lubricated enough⁩⁨Pump not pumping enough⁩⁨Pump shaft worn⁩⁨No strainer, scrap got in⁩

Where would you fix it?

Fix at why 5: install a strainer. That was Ohno's fix: with no scrap getting in, the chain above it has nothing to start from.

Ohno's chain from the example, one answer per layer. Pick the layer you would fix, and the gold root shows where the problem stops coming back.

Definition

5 Whys is a questioning method for finding the root cause of a problem. You state the problem, ask why it happened, then ask why about that answer, and keep going until you reach a cause that, once fixed, stops the problem from coming back. Five is a guide, not a fixed number: sometimes three questions are enough, and sometimes more are needed. The method is credited to Sakichi Toyoda and was used at Toyota as it developed its manufacturing methods. Taiichi Ohno formalised it in the Toyota Production System and called it the basis of Toyota's scientific approach. 5 Whys is one technique of root cause analysis, not another name for it. It follows a single chain of causes, while a fishbone diagram branches out to many possible causes at once.

Why it matters

Asking why repeatedly moves you past blaming a person to the gap in the system, such as a missing checklist, unclear instructions or a faulty tool, and that gap is what you fix. The method has known limits. Teruyuki Minoura, a former Toyota managing director, called it too basic to reach root causes at the depth needed, and Alan J. Card argued in BMJ Quality and Safety in 2017 that the fifth why has no principled link to the root cause. When a problem has several causes at once, or the chain keeps splitting, switch to a fishbone diagram. Either way, the answers are better when you ask why where the problem happened, with the people who were there.

Directly related: PDCA, Genchi Genbutsu, Pareto Principle (80/20 Rule).

Improvement tips

  • Write the problem down as one specific sentence before the first why, for example which order went wrong and when.
  • Assemble the people who are directly involved and ask the questions where the problem happened, not in a meeting room.
  • Use facts and evidence to answer each why, rather than relying on guessing or assumptions.
  • Focus the answers on process failures rather than blaming individual team members.
  • Stop when you reach a cause within your power to fix, then keep it from recurring with a poka-yoke or a new SOP.

Common mistakes

  • Performing the analysis alone in an office without talking to the frontline staff who saw the issue.
  • Allowing the analysis to become a search for a person to blame rather than a process improvement.
  • Treating five as a fixed number and cutting the chain short, or stretching it, just to reach it.
  • Using 5 Whys on a problem with several causes at once, where a fishbone diagram fits better.

Related terms

OperationsIntermediate

PDCA

PDCA (Plan, Do, Check, Act) is a four-step improvement cycle: plan a change with a prediction, try it, check the result, then adopt the change or drop it.

OperationsBeginner

Genchi Genbutsu

Genchi Genbutsu is a Toyota principle: before you decide, go to the actual place, see the actual thing and check the facts yourself, not in a report.

OperationsIntermediate

Pareto Principle (80/20 Rule)

The Pareto principle, or 80/20 rule, says a small share of causes usually produces most of the results, such as a few products bringing in most of the profit.

OperationsBeginner

Poka-Yoke

Poka-yoke (Japanese for mistake-proofing) means designing a process so an error cannot happen or is flagged at once, like a SIM card that fits only one way.

OperationsBeginner

SOP

An SOP (Standard Operating Procedure) is a written step-by-step guide to a routine task, so everyone gets the same result. It lists purpose, owner, steps, date.

OperationsIntermediate

Gemba

Gemba is Japanese for the actual place where work is done, like the shop floor, a counter or an inbox. It is where value is created, not where it is managed.

Quick check

Why is it important to ask why multiple times when a problem occurs?

Choose an answer

Frequently asked questions

Do I need to use the 5 Whys method before I launch my startup?
You do not need to run formal root cause analyses before launch because you do not have running operations or customer errors to analyze. Focus your energy on building your prototype and finding your first customers. You can start using this method once you have operational errors to fix.
How can a new business founder use the 5 Whys to test assumptions?
You can use this method to check why a potential customer is refusing to buy your product or service. Asking why they said no, and then asking why to their response, helps you find their true purchasing concerns. This direct feedback keeps you from building features that do not solve their real needs.
How long does it take to run a 5 Whys analysis for a small team?
For a simple problem, a 5 Whys analysis is one short conversation with the people involved. It does not require long meetings, reports or complex diagrams. If the chain keeps splitting into several causes, the problem is bigger than one conversation, and a fishbone diagram fits better.
Do I need to ask why exactly five times in every analysis?
You do not need to ask why exactly five times, as the number five is just a general guideline to help you dig deeper than the surface symptom. You might find the root cause after three questions, or it might take seven. Stop asking when you reach a process failure that is within your power to fix.
Why do the same customer errors keep happening in my business after I fix them?
Errors repeat when you only fix the surface symptoms rather than the root cause of the problem. For example, blaming an employee for a mistake might resolve the immediate error, but it does not fix the confusing procedure or lack of training that allowed it to happen. You must dig deeper to update the underlying system.
How do I run a 5 Whys session without my team getting defensive?
Keep your team from getting defensive by focusing the discussion strictly on process failures rather than individual mistakes. Frame the questions around why the system allowed the error to happen, not who made it. This keeps the focus on improvement rather than blame.
How do I know if I have reached the true root cause of a problem?
You have reached the root cause when the answer reveals a broken process, policy, or lack of standard guidelines that you can physically change. If your final answer is human error or bad luck, you have not dug deep enough. Keep asking why until you find a systemic gap you can fix.
Why is it a mistake to run a root cause analysis alone in my office?
Running the analysis alone is a mistake because you will miss the actual operational details that only your frontline staff saw. You might make incorrect assumptions about why the error occurred, which leads to designing useless fixes. Always gather the employees who were directly involved in the issue to analyze it together.
What is the 5 Whys technique in simple terms?
The 5 Whys technique means asking why a problem happened, then why again, until you reach the real cause. For example, a customer got the wrong order. Why? The wrong item was packed. Why? Two products look alike on the shelf. Why was it not caught? Nobody checks the order before it is sealed, because there is no packing checklist. The fix is the checklist, not a warning to the packer.
Is 5 Whys a difficult method?
The 5 Whys method is simple and requires no math, software or special business training. It is a structured conversation where you keep asking why to trace a problem back to its source. Anyone can run it with a notepad and the people who saw the problem happen.
Do I need to hire an external consultant to solve my business mistakes?
You do not need an external consultant or expert to find the cause of your daily business errors. You and your team are the best people to analyze the issues because you understand your workflows. Start by discussing a recent mistake with the team members who saw it happen.
What is the risk of stopping after the first why when a problem occurs?
The risk of stopping early is that you will only apply a temporary band-aid to the symptom, meaning the problem will keep returning. You will likely end up blaming an employee for being careless, which hurts morale without fixing the bad system. Digging deeper is the most reliable way to stop the mistake from coming back.

Sources: Taiichi Ohno, Toyota Production System: Beyond Large-Scale Production, Productivity Press, 1988 (Japanese edition 1978), Alan J. Card, The problem with 5 whys, BMJ Quality and Safety, 2017

Last reviewed: 2026-09-23

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