Triple Constraints Do Not Define Project Success

If you are a seasoned Project Manager (PM), you have heard of the Triple Constraints. The Iron Triangle, as it is also known, has long been the framework for PMs to evaluate and balance the competing project demands of schedule, cost, and scope. If you need more of one, you have to give up something on one or both of the other two.

PMs have used the Triple Constraints to define project success. Hit on-time, on-schedule, and on-scope, and your project is a “success.” But that is not the purpose of the Triple Constraints. Time, cost, and scope relate to project outputs, not project success factors. Using them to define project success fails for two reasons.

First, the Triple Constraints assist the PM in balancing competing requirements in order to meet the client’s defined success criteria, not to define success. If client goals are return on investment (ROI) and net present value (NPV), cost and time need to be optimized. If customer satisfaction and user adoption are primary, then scope and time to market need to be optimized. You end up sacrificing one to hit the others.

The Triple Constraint criteria also judge “success” as either yes or no, success or failure. Project success is not that black-and-white. Did the PM fail if the project was two weeks late? What if the project was two months long? What if it was two years long? What if you spent $100 more than budgeted? Does it depend on the total budget? Do we get to slip a certain percentage and still call it success? How is that defined? You won’t see that in the PMBOK.*

Second, and more importantly, project success factors are identified by the key stakeholders. They may be defined by customer satisfaction, end-user adoption, return on investment, regulatory compliance, and other business outcomes. The goal of the project is to deliver something that pleases your client. That is who defines success or failure, not the PM, and not the Triple Constraints.

In conclusion, the project’s customer defines project success. The Triple Constraints guide the PM in meeting the project customer’s goals by giving up in one area in order to meet objectives in another.