Environment Ladder
The ordered set of environments a change climbs, where each rung is justified by a distinct claim it can prove that the one below cannot.
Environments proliferate because each one was added for a reason that made sense at the time and none were ever removed. The ladder frames the question properly: for each environment, what does it prove that the previous one could not? An environment with no distinct answer is pure cost — infrastructure, data management, deployment time and the drift maintenance of one more configuration.
A defensible ladder is usually short. An ephemeral environment proves the change builds and behaves in isolation. A shared integration environment proves the wiring against real internal dependencies. A production-shaped environment proves contracts, performance and recovery. Production serves.
The rung that most often fails its own test is the one between integration and production-shaped: it holds neither realistic data nor realistic topology, so the things it could prove are proved elsewhere, and it survives because deleting an environment feels riskier than paying for it.