The term "root cause" refers to the underlying or fundamental cause of a problem or an issue. It's the core issue that sets in motion the entire cause-effect reaction that ultimately leads to the problem or event. 
The concept of a root cause is central to many forms of problem-solving. Quality control, for instance, is the object of a root cause analysis (RCA), a structured method used to analyze serious adverse events in various sectors such as healthcare, aviation, and IT. The purpose of identifying the root cause is to prevent the recurrence of the problem by solving it at its source.
For example, if a company is experiencing a decline in sales, it could be due to various factors, such as poor customer service, inferior product quality, strong competition, or ineffective marketing. By conducting a root cause analysis, the company could determine which of these factors is the root cause of the problem and then take appropriate action to correct it.
Understanding and addressing the root cause is crucial in problem-solving as it ensures that the same problem does not repeatedly occur. Treating a problem's symptoms often only provides temporary relief and does not prevent recurrence.
On the downside, identifying a problem's root cause can be time-consuming and complex. It often requires a multidisciplinary approach and the ability to look beyond the obvious to understand the systems at work that caused the problem.
- Definition - What is a Root Cause asq.org