As project managers, we are taught to manage the triple constraint of scope, schedule (or time) and cost (or resources). It is a way to teach PMs (and others) that there is no free lunch. If you want more scope, then you need to provide more time or more resources. If you want an earlier delivery date (that is, less time) then you need less scope or more resources.
It’s a good concept for beginning project managers. I lived by it for ten years or more. I was working on a project for a Fortune 50 company and my client kept adding scope. I had management reserve to handle a few scope changes but that was quickly exhausted. I spent a weekend developing an analysis that showed that we could no longer meet the deadline with the scope and resources. I was so nervous about the client meeting I brought the president of my consulting company with me to meet with the client. My client cut me off on slide 3 of a 19-slide PowerPoint deck. He said, “If you need more resources just say so.” I said I needed more resources. He added five developers and a development manager to the project within one week. Resource problem solved.
So the triple constraint is deceiving. First, because there may be NO constraints at all. Some companies, like my client above as well as companies such as Google, Apple and Microsoft, have a LOT of money. They can easily add scope and resources to a project. In fact, they usually do in order to achieve fastest time-to-market.
Second, the triple constraint leads some PMs to become an obstacle to achieving strategic goals. PMs all-to-frequently say no to every change request due to the triple constraint. Or they make the change request process onerous to discourage change requests.
The correct terminology is the triple trade-off. We PMs should be conducting trade-offs to ensure the project delivers maximum value to the organization. Ultimately, business value is what it is all about. Companies rarely care about scope, schedule and cost when the project is successful in maximizing business value. Trust me, no one cares if the original iPhone was delivered on-time or on-budget. PMs must know the business reason for doing a project and should base project decisions not just on the impact to schedule and cost but the impact to the strategic goals of the organization.