The Ishikawa diagram — also called the fishbone or cause and effect diagram — organizes the possible causes of a problem into categories, traditionally the 6M: Method (how the work is done), Manpower (people, skill, training), Machine (equipment, tooling), Material (inputs, components), Measurement (instruments, acceptance criteria) and Mother Nature, the working environment (temperature, humidity, layout, lighting).
The strength of the fishbone is that it is a tool for structured brainstorming: instead of the team going round in circles, each category pulls its own specific questions and stops whole angles from being forgotten. It does not point to the root cause on its own — it maps the hypotheses. The next step is to prioritize the most likely hypotheses and verify them with data from the process (or go deeper with the 5 whys).
The most common mistake is writing generic causes: "lack of training" helps nobody. A useful cause is specific: "the shift 2 operator was not trained on revision C of the packing instruction". Another mistake is stopping at a pretty diagram: without the step of verifying the hypotheses on the shop floor, the fishbone becomes meeting-room decoration. Finally, build the diagram with a cross-functional team — the value is in the different angles that each function can see.
Because graphical diagrams are hard to keep up to date inside a document, the table format below works better day to day: one row per hypothesis, with the category, the planned verification and the result. It is the same content as the fishbone, ready to become the root cause analysis record in an NCR or an 8D.