Is the classic triple constraint still relevant in project management?

Michelle Symonds contributed this guest post.
Michelle SymondsIn the following article:
What is the Triple Constraint?
Why are project constraints important
The problem with the traditional triple constraint in project managing
Different constraints for different projects
Changes in constraints have an impact

There are always constraints to projects. For example, there might be an urgent need to complete a project due to external market factors. Or there may be strict cost control requirements due to a fixed budget.
It is also expected that the project will meet certain standards, including quality.
What is the Triple Constraint?
The “triple constraint” was the most common planning constraint in project management. It is also known as the “iron triangle” or the “project management triangle”. It’s often depicted as a triangle with each vertex and the constraints at each end.
This video on the history and management of projects gives you a glimpse at Martin Barnes, the inventor of the Iron Triangle.
You could also see it as three interlocking circles with Quality in the middle.
However, quality is only one of three constraints in project management. Other constraints have been equally important.
Constraints can include factors such as risks, human and non-human resources, expectations, R&D or technology issues that could impact ground-breaking tech projects.
Many practitioners have made it a point to include Quality as a constraint in their project management models, since managing project constraints is a crucial part of project management.
It is becoming more apparent that even this doesn’t go far enough. A 6-pointed star (or more) is now proving to be a realistic constraint model for today‚Äôs projects.
Why are project constraints important
No matter what constraint model shape you choose, or which constraints are most important for a particular project, it is certain that any adjustment to one constraint will have an impact on the others.
If you assume that there are only three constraints, Time, Cost, and Scope, then it is obvious that increasing the scope of the project will have an impact on the time required to complete it and/or the project’s cost.
Equally, if you add Quality, Risks, and Resources to the mix, then changing just the scope can impact quality and potentially increase risk. This can also have an impact on resources.
It’s about balancing all the constraints that is essential to delivering a successful program. While it’s not rocket science, it continues to be a challenge for many projects.
Next: 5 Steps to Identifying Project Dependencies and Constraints
The problem with the traditional triple constraint in project managing
It is possible to manage a project with the three simple constraints of cost, time and scope. It may be possible for a simple project where the project manager and team have previous experience and the costs are well-understood and the scope is clear.
Even simple projects can be complicated if you introduce an element or team that isn’t familiar or a new manager.
If you introduce complexity, then the project’s success can be affected by the quality, expectations, resources, and risks. The triple constraint model may not be sufficient.
Like so many other elements in project management, the models provide a solid base from which to create a more tailored approach for each project and its circumstances.
Different constraints for different projects
While most PM practitioners agree on the importance of project constraints, details of each project are not.