The Project Management Triangle.
Like any human undertaking, projects need to be performed and delivered under certain constraints. Traditionally, these constraints have been listed as "scope," "time," and "cost".[1] These are also referred to as the "Project Management Triangle", where each side represents a constraint. One side of the triangle cannot be changed without affecting the others.
These three constraints are often competing constraints: increased scope typically means increased time and increased cost, a tight time constraint could mean increased costs and reduced scope, and a tight budget could mean increased time and reduced scope.
A further refinement of the constraints separates product "quality" or "performance" from scope, and turns quality into a fourth constraint.
The discipline of Project Management is about providing the tools and techniques that enable the project team (not just the project manager) to organize their work to meet these constraints.
