The costs that do not appear in the original business case
Large programmes consume executive time, project resource, IT effort, operational attention, change management, and supplier management capacity. When delivery runs long, those costs compound quietly.
Failure points are predictable
The same issues appear repeatedly: thin requirements, underestimated integration complexity, optimistic migration timelines, supplier capacity assumptions, weak governance, and unclear acceptance criteria.
Where independent oversight helps
Independent oversight is most valuable before and during the early stages of delivery, when programme-shaping decisions can still be changed. It protects the business case by making risk visible before it becomes expensive.