Triple Constraint Theory Fails in the Field; It's not just incomplete, it’s limiting performance and imprisoning project managers

The practical use of the triple constraints (or Iron Triangle), as a framework for managing projects, is not just limited and incomplete, it is negatively affecting the performance of project managers, project quality, and the success of projects.

The notion of a relationship between time, cost, and scope/quality is a simple construct that is good and useful when articulating the fundamental ideas of project constraints.  It can even facilitate discussions around comparing projects constraints (i.e., strong, middle and weak); however, it is rudimentary and lacks the depth needed to truly manage project constraints and ultimately project outcomes.

Even recent work that broadens the Iron Triangle into a diamond or star fails in practical use.  The TRIJECT Model (see Theory of the Triple Constraint – a Conceptual Review by C.J. Wyngaard et al.) which incorporates and unifies Dobson’s theory of the Hierarchy of Constraints (see M. S. Dobson et all, The Six Dimensions of Project Management) seems closer to practical usability than other models, but still fails to incorporate critical considerations. These modifications to traditional constraint theory (i.e., the triple constraints) have been made in reaction to recognized weakness in using the theory as a tool to help manage projects.

The project management profession has generally overused the Iron Triangle construct because of its simplicity and has failed to consider how deep constraint management applies in most projects. For instance, we often cite the “faster, better, cheaper; pick two” idea to a sponsor to set the stage for constraint discussions, but it’s never quite that easy.

We fail to recognize the far more critical organizational context in which a project exists or we accept the triple constraints as immoveable walls around our projects as created by our sponsors. This perspective leaves us in a position where we manage by allowing movements within constraint hierarchy or where a negative shift in the cost, time or scope/quality wall represents failure; always from the perspective of a prisoner held captive to these rudimentary project constraint models.

When performance of the project management industry is measured using this model, we are told that 31.1% of projects are cancelled before completed, 52.7% of projects cost 189% of their original estimates (The Standish Group), and only 16% of projects in the IT space complete on time and on budget (Gartner Group).  Gartner cites that a mere 30% of projects that companies start actually achieve their aim.  Even worse, after decades of observing and experiencing these disastrous results first hand, agile development methodology practitioners want nothing to do with project managers and executives accept this rate of failure as “baked in” to their project management organization.

[This was excerpted from our recent submission to PM Magazine.  Jeff Welch and I welcome critical comments and we will respond. Part II of the article will be posted next week.]