Three factors constrain every project. They exist in a state of equilibrium. One factor can’t change without one or both of the other two factors changing (like the sides of a triangle).
The three sides of the triangle are the three variables that define all projects: delivering a scope of work, on schedule, and on budget.
When one side of the triangle changes, we must adjust one or both of the other sides to ensure project success. This is how we prevent scope creep, the silent killer of successful projects.