5 Whys in practice


For want of a nail, the shoe was lost,
For want of a shoe, the horse was lost,
For want of a horse, the rider was lost,
For want of a rider, the message was lost,
For want of a message, the battle was lost,
For want of a battle, the war was lost,
For want of a war, the kingdom was lost,
For want of a nail, the world was lost
‘The Want of a Nail”

– T. Rundgren
Warner Chappell N.A., Ltd., 1989

We all must have read the above poem or heard about the proverb “For want of a Nail the kingdom was lost” at some point in our lives. Both the poem and the proverb illustrate anecdotally how disasters happen seemingly due to innocuous causes. It is fascinating how something seemingly unimportant could have caused great failures. It is also a subject of lots of research across the world for the past hundred years or so. Research to find solutions which prevent these tiny errors that cause cascading yet seemingly minor effects in a complex system that eventually cause it to fail.

Many effective solutions, methodologies and frameworks have come out from that research. 5 Whys is one of those frameworks. The definition of 5 Whys is as simple as it sounds, it is just a process of asking the question why 5 times. In practice it is a lot subtler than that, as you will see further in this blog.

It is, simply put, an iterative way to discover root causes, hidden or otherwise.

A more formal definition can be found on Wikipedia.

5 Whys is an iterative interrogative technique used to explore the cause-and-effect relationships underlying a particular problem.[1] The primary goal of the technique is to determine the root cause of a defect or problem by repeating the question “Why?” Each answer forms the basis of the next question.

This blog goes into detail about how to effectively use 5 Whys in practice.

This technique was developed in the 1930s by Sakichi Toyoda one of the early pioneers of the Japanese industrial revolution.  He was an inventor, industrialist and was the founder of Toyota which uses this technique to solve problems to this day. Infact the 5 Whys technique was so effective that another Toyota pioneer Taiichi Ohno in his book Toyota Production System: Beyond Large-Scale Production,  says that it is “the basis of Toyota’s scientific approach”

The picture below is an illustration of the 5 why’s in action.


That is all there is to it. The key is in asking why something happened till we find a reasonable root cause, which itself is usually caused by something beyond our control

Now what if we had not asked why enough times in the previous case. We probably would have done one of the following.

  • ‘Un-tripped’ the machine from overload: The machine would have run fine till the next time it tripped because of overload. In the long term we would have damaged the machine by over using it in spite of it being overloaded.
  • Change the oil pump drive: Doing this would have solved the problem for some time until the new oil pump drive ‘wears out’

Here in both the cases we took some action which would solve the problem only temporarily and the problem comes back sometimes in a more severe form or accompanied by one or more new problems. This could have been avoided if we would have spent time analysing why the problem itself is happening in the first place instead of directly jumping to fix the visible symptom.

We need to temporarily suspend our thinking of  “How to fix the problem ?” and start thinking “Why is the problem occurring ?” and when we get an answer we start over again by suspending the “How to fix it” thought to think about “Why is it occurring”. Then repeat until we find the real root cause of the problem.

Before I conclude, here are a few points that one needs to keep in mind while using the 5 Why technique.

  • The number 5 is not set in stone:

While the technique recommends asking why 5 times it may so happen, that you found your root cause before the fifth why was asked. It is also possible that it took more than 5 whys for your root cause to be found. This is subjective and depends on your core problem.

You are the best judge of what your reasonable root cause is. A rule of thumb is whether you can do anything about your root cause. For example, lets assume that you have down time because of spare-parts not being available in your warehouse because of a labour strike in the country where the factory which produces your spare parts is located. You probably cant do anything about a strike in a foreign country. Then an exercise on finding the whys behind the strike happening in that country would probably be futile. Then your reasonable root cause is the lack of reserve spare parts. Also if you find that a root cause is something you can fix, there is no harm in asking a 6th or a 7th why till you reach one that is beyond your control.

Although one thing to remember is if too many of your 5 Whys sessions are ending in 1 or 2 whys or you are ending up with root causes that are way out of your control, then you may not be doing 5 Whys correctly.

  • The root cause is not the only thing that needs fixing:

If A is caused by B which is caused by C which in turn is caused by D and you find that D is your reasonable root cause, then the first obvious step is to fix D. Also in many cases it might be prudent to make sure that If D happens, then that shouldn’t lead to C happening which in turn should not cause B and B shouldn’t cause A.

In summary, while the purpose of the 5 Whys exercise is to establish causality, your resultant action should be counter measures that not only prevent the root cause but also break as many links as possible in the chain of causality from the root cause to your problem. Many people fix the root cause and neglect breaking the chains of causality.

  • Multiple Applications:

Because of its simplicity, 5 Whys can be used in a lot of places. It can be used for personal improvement,  sprint retrospectives and fact finding enquiries both corporate or otherwise. The only thing to remember is to keep finding causes till we find the root cause.

  • Not only for retrospecting failures:

Although it is predominantly used for finding root causes to problems or failures, it need not be the only place we use it. It can be used even to study successes. A 5 Whys inquiry is about finding a chain of causes and arriving at a root cause, no one says that the root cause should only lead to a failure.

It can be used to find reasons behind an unexpected success so that the ingredients of that success can be replicated. It can also be used – for example – to compare,  contrast and find out the real hidden differences between two systems that seem to give different outputs when inputs and preconditions seem to be same.



  • The picture above illustrating 5 Whys is taken from this awesome blog post on the same topic.
  • You can read more about the proverb ‘For want of a nail’ here.
  • The Wikipedia definition of 5 Whys is taken from… well wikipedia.