Problems with the PMBOK® Guide Definition of Project Constraints


This is a text of a speech I will give today at the Orange County Project Masters’ Toastmaster meeting.

1. Challenge Disaster

On January 28, 1986, the space shuttle Challenger broke up 73 seconds after launch, causing the death of 7 crewmen aboard. The Rogers Commission was established to find out the cause of the disaster.  The technical reason for the disaster was the faulty design of the O-rings on the solid rocket booster. But one of the members of the commission, Richard Feynman, the legendary theoretical physicist, dug deeper to find the root cause of the problem.

He found that NASA management lacked understanding of some scientific and engineering principles, including the project management principle of “the iron triangle of constraints.”

2. Iron Law 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.

3. Challenge Disaster—Root Cause Analysis

This is exactly what NASA’s management did. They were given a reduced, but then they turned around and expected the same level of scope of the project with the same schedule. They asked for one variable to be constrained, and said that it should not affect the other constraints. That is impossible, and their decision had with fatal consequences.

4. Project Constraints—definition complete, but not coherent

Given this extremely important principle of project management, I was very dismayed to find that when a PMP exam prep course was put on this summer by the OC chapter of PMI, many people found it hard to understand. I wanted to find out why. I looked at the PMBOK® guide’s explanation of “constraints”, and looked at some PMP exam guides like the one put out by Rita Mulcahy. I found my answer there: gone is the simple iron triangle. Their definition of “project constraints” listed six or sometimes seven constraints. People say they can’t remember all of the project constraints, and they are the relationship between them is not clear. In trying to make the list of constraints more complete, they lost the consistency or coherency of the definition, because the simple connection between constraints which is at the heart of the principle was now obscured.

5. The Incompleteness Theorem

What they unwittingly ran into was another conflict of constraints, but this one due to the structure of logic itself. A man named Kurt Gödel in Germany in the 1930s discovered the Incompleteness Theorem which today bears his name, and this discovery shocked not only the scientific world, but the world of mathematics as well. What it says is that a mathematical or logical theory has two constraints, it can be complete, which means that it contains all the necessary elements, or it can be consistent or coherent, which means that it contains all the necessary connections between the elements, but it cannot be both 100% complete and consistent.

I’m not here to give the technical details of the proof, but I can a tantalizing glimpse of how it works.

Here’s a 3-by-3 matrix of dots. Can you draw a connection between all of the dots with a series of only 4 connected lines? If you try it, you will find that the only way to solve the problem is to go outside the framework of these dots. In order to make the connections between the elements and make it coherent, you have to admit the original framework of elements is not complete and go beyond it.

6. Project Constraints Definition: emphasis on completeness → lack of coherence

In any case, what does this Theorem have to with the theory of constraints in project management? The original iron triangle of constraints had three variables, and three connections between them (the three sides of a triangle). It was consistent; people understood it. One member of the study group was asked in an interview, “what are the basic constraints on a project?” Luckily, she had learned about project constraints in the “old school” way as the iron triangle, and said, “why that’s simple: time, cost and scope.” Others couldn’t answer that simple question. She got the job, by the way.

But at some point, the Project Management Institute felt that they wanted to make the list of constraints more complete, that is, they wanted to more and elements to the list. So they added quality, risks, resources, and even customer satisfaction. The problem now is the list is more complete, but the relations between them are now not so clear, the coherence is lost.

Now what if my friend from the study group had answer the question based on what she had studied in the PMBOK Guide. “Well, they are arranged in a seven-sided polygon and using the formula n(n-1)/2, there are 21 possible relationships between them.” That answer would have been met with non-comprehension at best.

7. Summary

So it’s important for PMI to understand that when you try to teach project management principles to aspiring project managers, if add more and more material to a theory or definition, it’s like barnacles that encrust the outside of a ship making it harder to go through the water. In reality, all of those additional constraints that PMBOK lists can all be understand to be aspects of the scope of the project. In other words, inside this complicated heptagon is the same simple, easy-to-understand triangle.

In summary, when teaching vital principles of project management to people, the best method may be summed up in the acronym KISS, the polite version of which can be read as keep it short and simple. Make your explanation COHERENT so that people can FIRST understand the principle 100%, and then and only then worry about it being 100% COMPLETE.

One Response

  1. You have to read again G:odel.

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