Getting to the Root Cause by Asking “Why?” Five Times

An integral part of kaizen is Toyota’s famous five-why analysis. I recall interviewing Yuichi Okamoto, a former Toyota Technical Center vice president, about the secret to the success of Toyota’s product development system. I was expecting a description of a sophisticated process similar to the TPS. Instead, he answered with an underlying tone of sarcasm, “We have a very sophisticated technique for developing new products. It is called five-why. We ask why five times.”

The reason for Okamoto’s sarcasm is that there are no complex tools and techniques to explain Toyota’s success in product development. Many people are surprised when I give talks and tell them that Toyota does not have a Six Sigma program. Six Sigma is based on complex statistical analysis tools. People want to know how Toyota achieves such high levels of quality without the quality tools of Six Sigma. You can find an example of every Six Sigma tool in use somewhere in Toyota at some time. Yet most problems do not call for complex statistical analysis, but instead require painstaking, detailed problem solving. This requires a level of detailed thinking and analysis that is all too absent from most companies in day-to-day activity. It is a matter of discipline, attitude, and culture.

Taiichi Ohno emphasized that true problem solving requires identifying “… ‘root cause’ rather than ‘source;’ the root cause lies hidden beyond the source.” For example, you might find that the source of a problem is a supplier or a particular machining center—the problem occurs there. But what is the root cause of the problem? The answer lies in digging deeper by asking why the problem occurred. Asking “Why?” five times requires taking the answer to the first why and then asking why that occurs. Typically, the process of asking “Why?” leads upstream in the process. It may be a defect that occurs in assembly, but the root cause is upstream in the raw material supplier, where the variation in the thickness or hardness of steel affects how the part is stamped, which then affects the way it is welded, which then affects the ability in assembly of the fastener to hold the part in place.

Provides a hypothetical example of five-why analysis that Toyota uses in internal problem-solving training. The problem is oil on the shop floor. In this example, each why brings us further upstream in the process and deeper into the organization. Note that the countermeasures are completely different depending on how deeply we dig. For example, cleaning up the oil would simply be a temporary measure until more oil leaked. Fixing the machine would be a little longer term, but the gasket would wear out again, leading to more oil on the floor. Changing the specifications for gaskets could solve the problem for those particular gaskets, but there is a deeper root cause that would still go unresolved. You could purchase other parts at lower cost, based on inferior materials, because purchasing agents are evaluated based on short-term cost savings. Only by fixing the underlying organizational problem of the reward system for purchasing agents can we prevent a whole range of similar problems from occurring again in the future.

A five-why analysis of a real problem within the Toyota Technical Center (TTC) provides another illustration. The manager of information systems developed a plan to convert to a new e-mail system with new features such as extended external e-mail capability and room scheduling. He devised the plan by identifying the weaknesses of the current e-mail system and compiling new capabilities that users wanted. Through a bidding process, the manager found an e-mail system he was pleased with and got approval to purchase it. When they installed the e-mail system, the manager sent out manuals to all employees and had them sign a letter confirming they had received one. One month later, the manager received many complaints from employees who did not understand all of the functions and found the manual too difficult to read. The manager met with the technicians and system analysts and they decided as a countermeasure to provide training. The training was viewed as helpful, but one month later, the manager still had numerous complaints about the same problem of understanding functions and the poor manual.

What was the real root cause of the e-mail complaints? Shows the result of the five-why analysis at TTC. In this case, the surface problem was that employees were not happy about their understanding of the e-mail system and the poor manual provided. As they got deeper and deeper into the root cause, they discovered that the manager had not followed the Toyota Way principles of genchi genbutsu and nemawashi discussed in Go and See for Yourself to Thoroughly Understand the Situation and Make Decisions Slowly by Consensus. The manager had not done enough work going directly to the source and studying how people use e-mail or the manual. He did not develop a deep understanding of the situation (genchi genbutsu) and he failed to pilot the process. A well-executed A3 reporting process could have avoided the problems. When they dug even deeper, asking “Why?” TTC discovered this failure to follow principles occurred because senior management failed to create a culture that supported the Toyota Way. The final countermeasure resulting from the e-mail incident was to include training and a great deal of follow through by senior management to build a culture supporting the use of good internal processes that follow the Toyota Way.

What is the real learning point of these two cases? To keep asking why until the root cause(s) are determined. Take countermeasures at the deepest level of cause that is feasible and at the level that will prevent reoccurrence of the problem.