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When a Bug Appears, the Most Dangerous Thing Is Finding a Cause Immediately
The first plausible explanation is only a falsifiable hypothesis; a root cause must survive evidence and guide prevention.
A system throws an error, and someone quickly says, "It is probably the cache." The sentence may be right. The danger is that it sounds too much like an answer. Once the team accepts it, every action circles the cache: clear it, restart it, change the expiration. The error disappears once, and the conclusion appears confirmed.
But "the error stopped after the change" only shows that an intervention and an outcome happened together. It does not prove the intervention addressed the root cause.
Keep more than one explanation alive
A saved essay compares an unresolved problem to a dumbbell: putting it down too quickly prevents any training. I prefer to translate that metaphor into an engineering action—keep several explanations that can be disproved.
Google SRE's postmortem guidance emphasizes blameless review, sufficiently detailed root-cause analysis, and action items that are actually carried out. The purpose is not to find a person or component to blame first. It is to let evidence support a change that prevents recurrence.
Evidence should be able to eliminate a hypothesis
Consider the cache example. At least three explanations can coexist: stale values exist in the cache; the cache merely amplifies a slow database query; or the restart temporarily lowers concurrency. Each explanation needs different evidence and a different falsification condition.
If clearing the cache removes stale values while database latency remains stable, the first explanation gains support. If the error returns whenever concurrency recovers, the cache may only be a surface symptom. If the same request still times out while bypassing the cache, the search should move downstream.
Writing these conditions takes a few more minutes than saying "it looks like the cache," but it can prevent the same incident from returning.
A cause must point to a durable change
I prefer to separate cause into three layers: what triggered the incident, which system conditions allowed it, and which change can stop it from recurring. The layers may point to different things; they do not need to fit into one slogan.
The root cause is not the earliest explanation. It is the explanation that remains after attempts to disprove it and still points to an effective change.
Sources: To Make Money, Go Crazy First?; Google SRE: Postmortem Practices for Incident Management.