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DEBUGGING-FUNDAMENTALS5 MIN READ

Use 5 Whys With Evidence

Apply 5 Whys only when each why answer is backed by evidence and leads to a controllable system fix.

The nightly invoice job skipped 312 customers after a billing schema migration. 5 Whys with evidence: every why answer needs proof, and the final countermeasure should improve the system. The common trap is stopping at the first human action: Alex forgot to update the script. That may be true, but it is rarely deep enough to prevent recurrence. A blame-shaped answer makes people hide information and leaves the process unchanged. Why 1 Why were 312 customers skipped? The invoice job filtered out rows where billing_plan_id was null; logs show those rows were excluded at 02:14. The answer uses job logs,…

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