The five diagrams ask five questions that cannot be answered by the same drawing.
| If you want to know… | Draw this diagram | Not this one |
|---|---|---|
| Where latency comes from | D1 Request Flow | D2, D3, D4 — they do not show the synchronous request path |
| What happens if a disk fails | D2 Data Storage | D1 — it shows traffic, not data durability |
| What happens if a service crashes mid-message | D3 Event-Driven | D1 — it shows the synchronous path, not async coupling |
| How stale the analytics dashboard can be | D4 Data Pipeline | D1, D2 — they do not show data freshness in pipelines |
| What happens during a network partition | D5 Distributed Coordination | All others — none show the partition failure path |
The D5 diagram is the most commonly omitted and the most commonly needed in post-mortems.