Weekly incident reasoning / Vol. 01
Root Cause studies the investigation—not just the outage. Real evidence, wrong turns, decisive tests, and the reasoning that finally narrowed the fault domain.
Read this week’s caseApplications · Complexity 5/10
ThousandEyes examined a broad Meta outage affecting Facebook, Messenger, WhatsApp, and later Instagram. The most valuable reasoning move was showing that frontend network reachability remained normal while application errors and timeouts rose, which excluded one major fault domain immediately.
The diagnostic chain
What users and systems actually reported.
The first plausible explanation—kept provisional.
The observation that narrowed the fault domain.
The moment the investigation changed direction.
The mechanism that survived the evidence.
Previous investigations