Nice post on Root Cause Analysis:
This, more rigorous and long-lasting, approach to solving problems is called Root Cause Analysis. There are several tools that can aid in the process of Root Cause Analysis. One common tool developed by Toyota is called “5-why’s”. Basically, it is a simple approach of asking “why” several times until you arrive at an atomic but actionable item. To visually view the process of the “5-why’s”, a tool called an (Ishikawa Diagram) or a (Cause-and-Effect Diagram) or a (Fishbone Diagram) is often helpful — this tool is referred by either of these.