A target architecture is a diagram until somebody provisions the landing zone, works out how identity federates, decides what an isolated environment actually means for this estate, and runs the migration without dropping a transaction. That work is where programs are won and lost, and it is the work most advisory firms hand to someone else.
The consequences are specific and expensive. Access models designed on a slide fail the first security review. Migrations sequenced without knowing the integration surface run twice. Cloud bills that looked fine in the business case arrive with a run-rate nobody modeled, because the architecture was never costed at the workload level.
We treat infrastructure as a first-class capability rather than the implementation detail at the end of a strategy engagement. The people who set your target state configure the environments, write the Terraform, design the access boundaries and stay on call while it proves itself.