Project Management Triangle (also known as Golden Triangle or Iron Triangle) has one missing part.

Originally, when the triangle was developed, the missing part was so obvious that the author didn’t include it in the triangle.

“I was thinking about how time control could be integrated with cost control. This was the main plank of my research (1959). I designed a computer program which did integrate cost, time and resources and could show the effect of decisions about the work and how to do it on both cost and time simultaneously.” (HOW IT ALL BEGAN, PM World Library, 2006, Dr. Martin Barnes)

The CPM method was invented (1957) as an attempt to understand how resource assignments impact project Time and Cost, but soon it was realised that the third component, quality, is also very important.

“…you did not just have to manage the cost and the time, you had to manage the delivery of what was specified as well. I sketched a diagram to make the point – a triangle with time, cost and quality at the corners. On the overhead projector, I moved a coin around the triangle to show how the three tensions competed, etc. This concept really caught on and, as far as I know, it was the first time anybody had set down that managing what we now call a project was not just time control, it was control of cost and outcome as well.”

The triangle is NOT ‘How Time, Cost and Quality impact each other’ but ‘How changes in Resource assignments impact Time, Cost and Quality.”

An alternative version of the triangle with “Time, Cost and Scope” was developed later, but it is a different story…