What it is for
In an accident or near-miss investigation the first cause found is usually the most visible one, and often not the root. A fishbone splits causes into groups so the investigation does not stop at the first answer: people, method, machine, material, environment and measurement are each questioned separately.
How it is built
The outcome is written on the right; the groups attach to the spine as bones. Within each group the question "why" is repeated until the answer falls outside the workplace's control. A branch that goes outside control closes there; every branch that stays inside becomes a candidate for a control.
The common mistake
Letting the diagram end at a person. "Carelessness" is not a root cause; the answer to why attention lapsed sits closer to the root — shift length, lighting, how clear the instruction was, where the equipment stands. An investigation that ends at a person does not stop the same event happening to someone else.
In Optifora
In the incident investigation flow the diagram is built against the event record; each branch becomes a finding and each finding a corrective action. The event does not close until an action with an owner and a date closes.