FM11 — Observability Blindness
The four-step method finds the algorithmic core from the outside. It assumes you can observe what the bottleneck operation is. When a system lacks instrumentation — no per-operation latency histograms, no queue depth metrics, no hit/miss ratios — you cannot complete step 1. You are guessing.
The method requires observability. Before you can identify the algorithmic core, you need measurements that tell you which operation is the bottleneck. A system without metrics is a system you cannot analyse.
FM6 — Hotspotting
Naming the algorithm does not automatically reveal which instance of the algorithm is being run. Hash-based routing is O(1) — but with a naive hash function, two-thirds of requests might route to the same three servers out of twenty. The complexity class is correct; the constants are wrong.
The algorithm tells you the class of the problem. It does not replace measurement.