That is, if Mr. A has credibility. Bill, for example, had previously completed several projects on schedule and Vin trusted him and believed what he said. Suppose, for example, that Mr. A has already completed several projects on or ahead of schedule. Now, if Mr. A says that a job will take four months, Ms. B probably would not argue. She might ask for supporting data but she has learned that Mr. A does what he says he will do, and he does it on his committed schedule.
Credibility is powerful.
Once engineers have it, they can debate schedules from a position of strength. When they give a date, everybody believes them. In fact, the engineer with credibility is like a magic planning tool, only one that is specially tailored to the work to be done. The managers just ask the credible engineer how much time and resource the job will require, and voila, they get a date they can count on. While it may take a little time for the engineer to produce a plan, when they get it, they know they have something worth waiting for.