The Five Whys also named 5-whys analysis method is used to isolate the true root cause of a problem.
When disecting a problem, ask why the issue occured. For each reason given, ask why that reason happen. After asking why repeately for every reason, you will identify the true root cause.
5 why means 5 cycles, but you may not need 5 cycles. Sometimes 3 or 4 cycles isolates the cause. By the time you get to the 4th or 5th why, most likely you're looking squarely at management practices.
This methodology is closely related to the Cause & Effect (Fishbone) diagram, and can be used to complement the analysis to complete a Cause & Effect diagram.
Here is a real world example from a kitchen manufacturer:
Root Cause: Company management did not understand lean manufacturing, and did not set appropriate project targets when the plant was launched.