The migration was delivered on time. The architecture diagram was sound. Six months later the capacity bill had grown 40% and a third of the workspaces had no active users. This is the post-mortem, anonymised and with numbers.

We reconstruct the timeline of a real Fabric adoption: which decisions drove capacity consumption and which ones nobody linked to cost until the invoice arrived; how workspace and domain design quietly became sprawl without anyone deciding it; which artefacts were abandoned and why; and what the usage telemetry showed against what the steering committee had been told. Along the way, the instrumentation that would have surfaced each problem months earlier — CU metrics, lineage, ownership, activity — and the four decisions that, taken differently, would have changed the outcome.

This isn't a design session. It's what happened when the design met the organisation.