Project Practitioners > The Iron Triangle is alive and well!

The Iron Triangle is alive and well!

By J LeRoy Ward

Anyone involved in project management knows what the Iron Triangle is. It represents the traditional triple constraints evident in every project: namely, scope, time and cost.

Screen Shot 2015-03-29 at 11.05.07 AMFor years project management publications and standards, such as the Project Management Institute’s (PMI) A Guide to the Project Management Body of Knowledge, included a discussion of the triple constraints providing detailed information on how changes in one of the constraints affected the other two. Any PM course worth attending would address the triple constraints in detail to make sure the participants had a fundamental understanding of its dynamic and competing forces. 

Then something happened. 

The triple constraints fell out of favor. Academics and practitioners alike argued that there were more constraints than just three and that the triple constraints had become obsolete. Proponents argued that other constraints existed and many articles, and even a book or two, argued that the “value” the client received from the project trumped the triple constraints as if value was divorced from scope, time and cost. I never worked for a client who didn’t “value” a project that came in on time, on budget, and met all the requirements, did you? 

I don’t doubt for a minute that there are other constraints on a project than time, scope, or cost. But if I think hard about it, I can take any other constraint and contextualize in terms of these three. Risk, for example, has a cost associated with it. Quality, which in my thinking was always embedded in scope, has time, scope and cost associated with it. In other words, I think the concept of the triple constraints still has a lot of merit and that it’s dangerous to think otherwise. 

I say this because of what I observe in practice over my 40 year career. For example, the triple constraints are firmly embedded as contract requirements for a whole host of different types of work, from infrastructure to IT projects. I’ve met many project managers whose bonuses are, in large part, based on their ability to “beat” the constraints as it were. And, all the studies on project failure authored by Gartner, Standish, Forrester, and others almost always use the lack of meeting the triple constraints as a definition of failure. 

But wait there’s more!

In the February/March edition of the Project Management Journal, Pedro Serrador and Rodney Turner, in their article “ The Relationship Between Project Success and Project Efficiency” describes how they surveyed 1,386 projects and found that project success “correlates moderately strongly” to the triple constraints.  In other words, if you meet or beat the constraints your project is considered a success. Project “efficiency,” they write, “is shown through analysis to be neither the only aspect of project success nor an aspect of project success that can be ignored.” (emphasis added). By the way “project efficiency,” as defined in the article is another term for the triple constraints. 


So, as I stand on my soapbox (in my home office!) I call on the next collection of earnest PMBOK Guide volunteers to reintroduce the Iron Triangle into the next edition. After all, it is alive and well, and if you don’t think that’s the case just ask a project manager whose bonus, and perhaps job, is riding on his or her ability to deliver the project requirements on time (or earlier) and on budget (or lower).

They’ll tell you all the talk of value is interesting, but doing the job well is the best value of all.


Not all comments are posted. Posted comments are subject to editing for clarity and length.

Defining project success in terms of scope, schedule and cost presumes that the "product" delivered will provide value to the customer/user and be of high quality (being maintainable and adaptable). What has changed is the realization that quality and value should be the goal and focus of the work to the goal, subject to the constraints of scope, schedule and cost.

Hi LeRoy,

I enjoyed your post, but would like to provide a point of view that runs counter to yours. Below are a few of the arguments I'll throw from my soap box to yours.

I appreciate your viewpoint that value is not divorced from the triple constraints. However, I've encountered situations where value delivery is severely inhibited for strict worship of the triple constraint. I've been involved in projects that delivered exceptional value to the customer which violated the triple constraint and others that delivered minimal, if any, value to the customer that fell within the triple constraint. So, while I do believe you cannot fully divorce value from cost/scope/schedule, focusing on customer value first is paramount in my experience.

Another issue I had relates to a project manager's bonus being "in large part" based on their ability to beat the triple constraints. The issue is that it's usually not the project manager doing the work. Basing project manager bonuses on beating the constraints can, and often does, lead to those project managers "beating" the team - often because the triple constraint was based on wish thinking and unrealistic expectations and over-optimistic estimates (perhaps to be lowest bidder to win a contract).

Simply because something can be measured does not mean that it should be measured. Granted, on construction projects, infrastructure projects, etc. value is either there or it isn't (we have a structure or we don't). However, on creative endeavors such as software development, a myopic and laser-like focus on the triple constraint can lead to long term team and organizational health degradation. It can also lead to declining innovation.

Personally, and I know what I'm about to say is heretical, I feel that the concept of the "project" has run its course - at least for creative endeavors like software development. It should be replaced by continuous and frequent delivery of value. In this sense, I'm referring to customer value not to the aspirational value number assigned by organizations internally. Too often, value is equated to profit. Revenue and profit are the outcome (the measure) of delivering value to customers, not the sole focus.

Thanks again for the post LeRoy.


I couldn't agree more!

From my perspective the triple constraints are core principles that underpin all the more recent 'constraints'.

Further, when I started looking at the roots of uncertainty in projects I found that they seemed to correlate well with the triangle.


Andrew, thanks for your comments. I appreciate your point of view. All the best.


First, thank you so much for your insights and perspectives on the topic. It's pretty clear you've worked on a wide range of projects and can see both the flaws and advantages of focusing on the triple constraints. A favorite example of mine as regards the constraints and value is the Sydney Opera House. It was vastly overbudget, late, and had to be redesigned once or twice. The architect was so irritated that he left and went back to Denmark never to return to Oz again (however, his son later returned and picked up a big award for him!). Even though it violated each of the triple constraints the "value" it has brought to the country is almost immeasurable. That said, most of us will never work on something like this. What I found very intriguing in your comments has to do with your thought about how the term, or even concept, of "project" is coming to an end, especially as regards SW dev projects. I think that's a very interesting perspective. I know, for example, that Cinda Voegtli, who runs, consults with a number of firms in Silicon Valley and beyond who don't call these work initiatives projects, who don't want heavy PM processes (think PMBOK), and who focus instead on strategic execution. I think you, and the folks she works with, are actually at the cutting edge of where PM (if I can even use that word anymore) is heading, at least for certain kinds of projects. Thanks again for commenting. Really appreciate it.

R.B. Really appreciate your thoughts. You look at the triple constraints and value in a most realistic way. We can't throw the triple constraints out with the bathwater (to butcher an old cliche) but neither can we think that value is completely wrapped up in them either.

Love it! Thank you.

To answer one of your questions, "Have you ever had a project that delivered the specs on time, on budget not be valued?" Most definitely. They got exactly what they asked for ... but not what they needed. Why? because the market changed or some early assumptions didn't pan out. At the market's rate of change, this is almost bound to happen.

That said, I agree the triple constraints are core. And I agree that all other "constraints" are derivatives of those three.

I think the root issue is with how we define "scope". I advocate that "scope" be defined as "Business results" rather than "Requirements specifications." It's the difference between outcomes and outputs. Similar and related, but can be a world of difference.

What is value then? Value is simply "bang for the buck," the "business outcomes" generated for "inputs of time/money", or the "return" on your "investment." At the end of the day, Value is how well you optimize the triple constraints ... in the eyes of the CUSTOMER, not the CONTRACT. Hence the Sydney Opera house was "worth it" even though it took more time/money than estimated.

I have managed many PM's over the years. Their goal is NOT to deliver ancient specs to an arbitrary date and budget. (That creates the beatings mentioned above.) Their job is to translate the talent of the team into giving the CUSTOMER the best value possible by optimizing the balance of outcomes (scope) for the investment (time + cost). And those are ultimately measured at the END of the project. We should still compare our performance to our baseline so WE can learn. And it is helpful over time across a portfolio of projects. But that delta doesn't mean squat to the customers of each individual project.

So I agree. Triple constraints are solid and sufficient.

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