Project Triple Constrains is namely the Scope, Budget and Timeline. You need these 3 fundamental items in order to proceed with a project. A change in any one of the component will affect the overall results. Such as a change of scope, it will affect the timeline because of the number of resources to be purchased. A change of timeline will extend the budget because of the number of resources involved.
However, it may be difficult to achieve in actual environment. If you are the project manager in a supplier environment, you will need to ensure the triple constraints are seriously dealt with.
On the other hand, if you are a project manager in an end user environment, you will tend to push the supplier to give you more quality at a much lower cost.
Thus, do you really practice triple constraints in reality?
Have you got yourself into such circumstances?