Brainstorm major categories of your process and workflow. Connect them to the backbone, in "ribs". No specific number of categories have to be created to describe possible problem areas. It may be helpful to prioritize the categories into most likely, likely, probable, maybe, and not possible. The team may then want to place ideas on category ribs, starting with the most likely category and working down the list. There may be contributing factors that do not fit into a single category. If a contributing factor fits into more than one category, place it in each of the categories being studied. In the end, a big picture that can resolve the problem may be apparent.
