Verify the root cause by tracing back up the chain

After reaching a root, work back up: does each "because" in the chain make logical sense?

Why it works

Five Whys chains can drift from the actual causal sequence into plausible-sounding but incorrect reasoning. The verification test is simple: read the chain upward using "therefore": "root cause X, therefore level-4 condition, therefore level-3 condition, ... therefore the original problem." If each "therefore" is logically sound and empirically plausible, the chain is valid. If any step requires a leap or an assumption, the chain needs refinement.

How to do it

1. Write the completed why-chain from root to problem.
2. Read it in reverse using "therefore": "[root] therefore [next level] therefore … therefore [problem]."
3. At each step, ask: "Is this a necessary and plausible consequence of the preceding step?"
4. Where the chain breaks, restart the why-chain from that break point.

Evidence

Reverse chain verification is an internal consistency check used in formal root cause analysis (RCA) processes in healthcare and engineering. It applies basic logic: if the causal claim is valid, it should run in both directions. (mechanistic)

Logical coherence does not guarantee empirical accuracy; a chain can be internally consistent but wrong if any factual premise is incorrect. Verification should include empirical checks, not just logical ones.

Common mistake

Skipping the verification step because the chain "feels right" — chains that feel right are exactly the ones most likely to have a motivated bias built in.