John Goodpasture has a post at his blog about simplicity and complexity. The story is that it is the job of the project manager (and the project team) to hide the complexity of the solution and make it appear as “simple” as the sponsor’s needs statement . John includes a presentation that explores the different views of the project and once again shows how “most likely” is not the same as the mean expected outcome.
Business value is not the same thing as project cost. One job of the project team is to maximize the net by keeping projects costs below the value of the delivered product. That requires managing risk and some statistical thinking.