FM4 — Data Consistency Failure: Choosing eventual consistency without understanding the consequences leads to anomalies users experience directly — stale inventory counts, duplicate charges, disappeared messages. Specify the acceptable staleness window before choosing eventual consistency.
FM3 — Unbounded Resource Consumption: Underestimating storage growth. Storage that looks manageable at launch becomes unmanageable in two years if the estimation was too optimistic. Build deletion policies, retention limits, and archival tiers into the design from the start.
FM6 — Hotspotting: Uniform distribution assumptions fail in practice. Users, content, and geographic load are never uniformly distributed. Estimation must account for peak-to-average ratios, not just averages. A system designed for average load fails at peak.