5 WHYs

Problem solving is a whole science. To solve the problem, you need to understand the root cause. It's not always simple to figure out the real root cause, so you'd need to speculate, search, suggest and fail till you get more information to define the root cause. Just re-trying the same thing again and again till it's fixed won't help.
There are different techniques to find the root cause. One of them is "5 WHYs".

5 Whys is an iterative technique to explore the problem and determine the root cause.
You start and continue asking iteratively 5 "Why...?" questions, every next question is based on the previous question and answer. The technique is based on correct answers for the previous questions. If answers are invalid or incomplete, it helps to detect them and stop moving in the wrong way. Instead, go back, find the right answer and continue with it.

However, the number 5 is not imperative and one can go beyond this and ask more questions.
This technique was originally developed and used within Toyota. It is a critical component of problem-solving training in Toyota.

Although, 5 Whys is a pretty good way to find a root cause, its actually doesn't mean that the real or correct root cause would be found. The reason is because every next why? question is based on answer to the previous. If the answer is incorrect, incomplete or subjective, the result of this process will be wrong. Thus, using this technique requires good problem and analytical skills.
One of the ways to prove that the root cause found after of 5 Whys is to repeat the process multiple times and use different questions and/or answer sources.

Another use of 5 Whys would be to represent the found root cause (in whatever way it was found), and give some initial prove that it's actually could be a root cause. Pretty often, it's not always clear that X is a root cause for issue A. But if one shows the process in style why A? -> B, why B? -> C, why C? -> D, why D? -> E, why E? -> X, this is much helpful.

In my opinion, 5 Whys are good not because they promise to get you to the root cause after answering some 5 whys questions. Answering just some questions not enough. More important to ask correct questions. But answering even correct question just 5 times often not enough. What 5 whys teaches us is just to start asking questions. More and more questions, usually you do not stop with 5 questions. And that are not only the why questions. You ask what? how? when? who? why else? More and more questions are asked, and more and more problem is understood. Then it's just simplified to 5 why questions.

There are a bunch of hints how to use this technique correctly:

• ask more than just 5 questions
• ask more than just why questions
• as result get as much answers and use as much sources as you can
• do not accuse someone, do not point your finger on someone, usually the problem is deaper than someones misbehaving
• see if the problem repeats, find commons and differences
• use someone to help you make a correct chain of logical explanations
• give as much ideas as you can, be creative in finding root cause
• first found root cause is not root cause
• use some journal or diagram to log everything; pretty soon you'd have multiple 5-whys questions with different answers, just will end you with wide why tree

Why tree is especially interesting, because it can help to find multiple root causes. Pretty often, during investigation you can find more possible problems and their root causes. Log them, try to cope with them before they actually happen.