You will hear people say that if you change one it must effect one (or both) of the other lines. This is great in theory and looks like it make sense when you stare at the triangle, but the reality is that many projects do increase scope and both the cost and time time are not allowed to change. So how do they do this amazing trick? The secret to this lies inside the the project triangle. They do it by exploiting the 'quality' of the deliverable produced. You do this in one of many ways that could include:
- Rush through the construction or development
2. Skimp on the system or user acceptance testing
3. Use of inferior materials
Even though you might have met the scope, cost, and time your project will have produced a mediocre product. You sometimes see the project triangle with the word 'quality' in the middle and that is just as important as scope, cost, and time. Factor all four areas of the Triangle
This is not to say you should not use the project triangle, but you definitely should not rely solely on it for a successful project without also monitoring quality. Probably the best place to address quality is through non functional requirements. Add quality requirements and get this signed off. Couple this with a good change process and you will be making something you can be proud of.