For example, you are working on the design of a building's HVAC system, and you are told what flowrate of air is expected in a particular area of the building. Your preliminary calculations indicate that ductwork would need to be so massive as to require a redesign of the walls of the rooms. You trace the flowrate requirement back to a particular client representative who had ventured the value of the flowrate only as a guess, but somehow it became embedded as a hard requirement. After consultation, it is determined that the flowrate requirement can be relaxed.

If the flowrate really was correct, then consider: what other ways are there of designing the ducts?

And if the flowrate isn't the problem, then is it the specification of the walls?