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In this blog post, I take a slight detour to expand on the subject of project constraints which is mentioned as one of the elements of Project Management, but which deserves a lot more attention for two reasons: it’s importance and the understated way it is presented in the PMBOK® Guide, which unfortunately belies that importance.

1. Definition of project management

First let’s take a recap of the elements of project management as listed in the PMBOK® Guide:

Fig. 1 Elements of Project Management

Managing the project constraints is one of the important elements of project management, and to understand its importance let us consider the history of the idea of “the iron triangle of constraints.”

2. The Iron Triangle of Constraints

Dr. Martin Barnes first described the iron triangle of constraints as far back as 1969 in terms of time, cost and output (what we today refer to scope).  These three constraints are strongly connected to each other, hence the name “the iron triangle.” To understand how this principle works, think of a water balloon in the shape of a triangle. One point of the triangle is the project’s time, the second point is the project’s cost, and the third point is the project’s scope, which can include such elements as level of quality on the project.

What happens if you squeeze one end of that water balloon? This creates increasing pressure on the other two ends. In a similar way if you constraint one of the three variables of time, cost, and scope, it will put pressure on the other two variables is why engineers have a popular saying “faster, cheaper, better—pick two”. This acknowledges that if you constrain one variable, one of the other two variables has to give.

What you cannot do is constrain all three variables at the same time. What happens if you squeeze a triangle water balloon on all three sides at the same time? A broken water balloon, or in terms of our analogy, a failed project.

The following then, is a diagram outlining the interaction between what I will call the “Traditional Project Constraints” of time, cost, and scope.

Fig. 2 Traditional Project Constraints

3. PMBOK® Guide Definition of Constraints

From the table of elements of Project Management listed above, the PMBOK® Guide gives the following as what I will call the “Modern Project Constraints”:

• Scope
• Quality
• Schedule
• Budget
• Resources, and
• Risk

However, if you look at other exam prep textbooks, you may see even MORE constraints added. For example, Rita Mulcahy’s PMP Exam Prep adds Customer Satisfaction as another constraint.

In reality, however, you could map most of the “Modern Project Constraints” on the same diagram as the “Traditional Project Constraints.” The only one that is not obvious is risk, but the reason why I put it under the same category as budget and resources is that managing risk involves putting a risk response strategy in place which itself involves additional resources, so it seemed the most logical category to include it in.

Fig. 3 Modern Project Constraints

The important thing to notice is that underlying the seemingly complicated laundry list of constraints is the simple triangular structure of the traditional “iron triangle of constraints.”

It is important to notice this because many project managers who learned project management a while ago still think of “project constraints” in these traditional terms, and some of them get frustrated that the newer generation of project managers are unaware of this “iron triangle”. I know of two people who were asked at their employment interviews “what are the triple constraints on a project?” One of them knew about the “iron triangle of constraints” and gave the response, “time, budget, and scope”. The other didn’t because she had thought in terms of the laundry list of constraints that the PMBOK® Guide now gives and she couldn’t think of which three constraints the hiring manager had in mind. The one who knew about the “iron triangle of constraints” could answer the question easily and she got the job; the one who didn’t know about it and therefore couldn’t answer the question did not get the job.

So don’t let the long “laundry list” of constraints fool you; there’s an underlying triangular structure there that you need to be aware of both in terms of understanding the basic interaction among the constraints and because of the history of the very notion itself.

The next topic is how project management in an organization relates to two hierarchies of management above it, that of program management and portfolio management.

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