DEPLOY sits between CONSTRUCT (building it) and DIAGNOSE (fixing it). Most deployment failures happen because developers skip directly from "it works" to "it's live" without the disciplined verification steps in between.
Phase 5, "Observe and Verify," is the one most people skip. They deploy, see no immediate error, and walk away. But production bugs often take minutes to surface: the first real user hits an edge case, a queue fills up, a rate limit kicks in. Ten minutes of watching logs after deployment catches problems that would otherwise become incidents.
The interactive checklist on Phase 6 is there for a reason. Every item represents a deployment that failed because someone forgot that specific step. The checklist is the cheapest insurance policy in software.