Most problems that surface in physical or business processes have one or two primary causes. Once these primary causes are identified, all energy is put into controlling or eliminating them. This is called a convergent approach , where the trivial causes are ignored and resources are focused on the primary causes only.
The convergent approach has a high success rate.
Fishbone diagrams can lead teams astray by encouraging a divergent approach: the temptation to identify and fix everything that might be causing the problem.
The divergent approach has a low success rate because no team has the resources to fix every potential cause.
Check out this example from ASQ.org, where a team documented potential causes for “lack of reported medication errors.” There are over 40 potential causes in this diagram – far too many to take action on. An analysis like this produces an impressive looking fishbone diagram, but can leave the team feeling like the problem is too big to tackle. This team would have been better off using a combination of 5-why and Pareto analysis to find the “short list” of predominant causes.