Branch the chain when you find multiple causes

When a "why" has two or more true answers, follow each branch separately.

Why it works

Real problems often have multiple contributing causes at each level of the chain. Following only one branch produces a partial root cause — a condition that contributed to the problem but was not the only one. Fix that root and the problem may reduce but not disappear, because the other branches remain. Branching the chain when multiple causes are real produces a more complete picture and prevents premature closure on a partial fix.

How to do it

1. When asking "why?" and finding two or more true contributing causes, draw both as separate branches.
2. Follow each branch independently to its own root cause.
3. Assess which root causes are shared across branches — those are the highest-leverage fixes.
4. Design the intervention to address roots shared across multiple branches first.

Evidence

Multi-cause root analysis is recognized in failure mode analysis (Ishikawa/fishbone diagram). Branching the Five Whys is an extension of the method that combines its depth with multi-cause breadth; it is endorsed in lean quality literature. (mechanistic)

Branching increases analysis complexity; for simple problems, branching may introduce over-engineering. Use it when multiple causes are genuinely active.

Common mistake

Choosing the most convenient branch and following it to the exclusion of others — the result looks like a complete root cause analysis but has solved only part of the problem.