Have you ever been on a project where the client was eager to add more and more features, but not so eager to add more budget and schedule? In my training and consulting engagements, it's amazing how many times I hear this type of complaint from project teams. I tell these teams that part of the answer for responding to this situation is to educate the client. Many of them just don't have a sense that when they ask for additional features, it actually takes the project team more time and effort.
Part of the education process for your client might involve the concept of the "triple constraint." At the end of the up-front planning process, you should have created an estimate of the work that will be completed and the cost/time and duration that are needed to complete the work. The client sponsor should have approved the document that contains the scope of work, estimated effort/cost, and the project duration. These three items form the concept called the "triple constraint." The key aspect of the triple constraint is that if one of the three items change, at least one, or both, of the other items need to change as well.
This concept is easy to visualize if you think of the triple constraint as a triangle, with the sides representing cost/effort, duration and scope of work. Here are a couple examples of how the concept works.
- If the scope of work increases, the cost/effort must increase, and the deadline may increase as well. This should make sense. If you have more work to do, it will take more cost/effort and perhaps a longer duration. It's possible that the duration can remain the same, but only if the cost/effort increases sufficiently to complete the new work within the same duration.
- The triple constraint works the other way as well. If you reduce the scope of work, the cost/effort will decrease and the deadline may decrease as well. If you don't have as much work to do, it should not take you as much effort/cost to complete.
- If you are asked to accelerate the project and complete it earlier than scheduled, it would also be logical to ask for less work. However, if you are asked to deliver the same work for less duration, the third leg of the triple constraint must increase to maintain the balance. You will need to increase cost/effort, perhaps by working overtime hours or perhaps by bringing in more resources to complete the same amount of work earlier.
Of course, one of the keys to making the triple-constraint work is that you have to have an agreement with your client sponsor on the scope of work to be performed and the cost/effort and duration to complete the work. If you don't have a formal agreement on these factors to begin with, then the triple constraint concept does not work.
I have also heard the triple constraint referred to as a "three-legged stool," which carries the same type of visual connotation. In the example of the stool, the three legs still refer to cost/effort, duration, and scope of work. The thought is that the three legs start off in balance once the sponsor agreement has been reached. If the length of one of the legs is increased (or decreased), the other legs need to change as well so that the stool remains level.