A common question, especially in industries that are just now learning the Lean Business System.
Problem solving is a kata - a set of core forms that we practice over & over, hopefully under the guidance of a capable sensei.
(At Lean Pathways we try to reinforce the problem solving & related katas through our Brain Booster pocket cards & apps)
When practicing the problem solving kata, we pull in the tools we need including, Five Why, Ishikawa, Process Flow Diagrams, SIPOC etc.
It's a mistake to structure any problem solving discussion in either/or terms.
It's not Five Why OR Ishikawa OR Process Flow Diagram OR FMEA.
To paraphrase Hemingway, "it's all true." We pull in what we need. Another common mistake is underestimating Five Why.
"Five Why is too simple for me. I want a more complex tool, because this is a complex problem. (And I am a very complex guy!)"
In consulting practice we've used Five Why to get to the root cause of complex design, supply chain and organizational problems.
Five Why is especially helpful when we've clearly defined a Direct Cause.
Often there are multiple causes, and we need to apply Five Why sequentially to get to the root cause of each.
A common failure mode is not understanding the three types of Root Causes - Inadequate Standard, Inadequate Adherence to Standard, Inadequate System.
These are derived from the splendid NASA and Loss Control literature & are invaluable because they point to actionable root causes.
In summary, problem solving is a kata and not unlike trying to hit a curve ball, shoot hoops, or hit a golf ball.
(All of which baffle me...)
You practice, practice, practice the core skills & movements.
Then, if you're very lucky, the day comes you can do it unconsciously.