The Iron Quadrilateral

You may well be familiar with the Iron Triangle of project delivery: time, quality, and cost are closely interlinked and trade off against each other. Any improvement on one of those aspects will put downward pressure on the other two.

“Faster, better, cheaper: you can only pick two” is the pithy version.

And that’s if it’s done well. You can be slow, worse, and expensive.

I like to break it down further to an Iron Quadrilateral of time, quality, scope, and cost. Quality and scope can trade off directly: do less but better, or more but worse. And they both trade off against the others.

Here, for the first time, is a quick sketch of it!

The central idea is that trying to lift any one of the four corners will put downward pressure on the other three.

There is complexity within time vs cost tradeoffs and constraints, related to the Preposterous Person Month (an updated Fred Brooks’ Mythical Man-Month). Internal cost and resource models often treat person-months as more fungible than they are in reality. And of course cost can be in terms of money or person-months, and it might take time to turn the one in to the other, or you may be able to spend more money and bring in an expensive consultant to get effort in quicker.

This all sounds doomy, but good stuff can get done in a timely and cost-effective way. I find this most useful at project planning, and invaluable when I’ve had an upset. If your project takes a major hit on one aspect, the other three points remind you what you could do to mitigate the effect.

Scope creep you can’t resist? You’ll want at least one out of more resource (i.e. higher cost), more time, or lower quality. Deadline brought forward? Cut scope, throw resources at it, and/or accept lower quality. Must improve quality? Think about more resource, more time, or reduced scope.

The most common hit in my experienceIME is a resource hit, often because of a budget cut or ` loss of staff time to the project. The go-to responses are extending time, reducing quality, and/or limiting scope. Or throwing resources in to replace the lost ones – which can work, depending on the person-month issue.

This is all viewing a project within its existing conceptualisation. Great project delivery like this is about making it happen within the box of constraints and assumptions. Great leadership requires knowing when you need a completely different box.

(This post is a slightly extended version of a Twitter thread responding to an original observation of the three-way tension in the context of change projects by the excellent Hugh Jones.)