The triple constraint revisited

Adrian Dooley Hon FAPM is the Lead Author of praxisframework.com – a free online framework of good practice in project delivery and a set of tools to help embed that practice with real effect.

Dr Martin Barnes first came up with his idea of the time/cost/quality triangle in 1969, partly as a means of bringing together different roles within an engineering management team that separately looked after the schedule, the costs and the output of a project. When training, he would move a coin around an overhead projector to illustrate “how the three tensions competed”.

While Barnes was the originator of the project management version of these three constraints, the idea of ‘good, fast or cheap, you can only pick two’ has been around for decades – or maybe centuries. The 19th-century philosopher John Ruskin is purported to have addressed the relationship between cost and quality when he said, “The common law of business balance prohibits paying a little and getting a lot – it can’t be done.” The purpose of the ‘Barnes Triangle’ is to illustrate the tensions between getting a lot, getting it cheap and getting it quickly. While that may seem obvious, project management is constantly plagued by the optimism bias that seemingly ignores this truism.

The triangle itself has been given various names: the Barnes Triangle, the TCQ triangle or my preferred title, the Triple Constraint. Sadly, somewhere along the line, somebody named it the ‘Iron Triangle’. This was one of the greatest disservices to project management. It demonstrates a complete misunderstanding of what the Triangle is all about and suggests that all three corners are fixed rather than there being a natural trade-off between the three.

As far as I can tell, the term ‘Iron Triangle’ was originally a description of the policymaking relationships between elements of the American political system in the 1950s. Its adoption as a name for the Triple Constraint may have originated in an article in 2010 when, also misleadingly, it was cited primarily as the basis for project success criteria rather than a mechanism to understand what is viable at the start of a project.

Returning to the development and history of the triangle itself for a moment, Barnes himself decided that ‘Quality’ was not the ideal name for one of the corners. After all, the quality of an output (as in fitness for purpose) also includes elements of how much you have to pay for it and when you can get it. His own later versions of the triangle replaced quality with ‘Performance’. Personally, I prefer the more common modern use of ‘Scope’, making the three constraints: Time, Cost and Scope.

When any model gains a wide exposure and common adoption, many people decide it can be ‘improved’. The result over the years has been quadruple constraints, quintuple constraints and even hexagonal constraints.

For me, the triple constraint is like the three primary colours of red, yellow and blue. These can be used to address the competing primary components of a project when setting priorities at the start. All the suggested ‘improvements’ are about adding hues – these are relevant but do not affect the primaries.

And so I come back to the great disservice done by calling this the ‘Iron Triangle’. This term implies there is no flexibility and that all three corners are fixed. Fixed parameters and rigidity are the traits that those who promote the idea of ‘traditional waterfall projects’ love to latch on to. The ‘Iron Triangle’ is apparently one of the problems solved by agile. The falsehood here is that the problem never existed in the first place so, in this respect at least, agile is not solving a problem.

The Barnes Triangle of time, cost and quality is just as relevant as it was in 1969. It has been refined into the Triple Constraints of Time, Cost and Scope and represents the primary colours of a project from which a full picture of multiple hues can be painted – once you have found the right balance between the primaries.

THIS ARTICLE IS BROUGHT TO YOU FROM THE Summer 2022 ISSUE OF PROJECT JOURNAL, WHICH IS FREE FOR APM MEMBERS.