Are you building a house, or just pitching a tent?
When you read about decision analysis models in case studies, they're usually described in the narrative as part of an epic process, one that begins with organizational angst and ends with a resounding consensus to pull the lever on that "irrevocable allocation of resources". Right, and sometimes that really happens! But more often, the allocation of those resources is gradual, and even when a single large chunk of capital has been committed, there are steps along the path where the project is reevaluated.