Requirements and the business case

We hear a lot about the necessity of finding the right requirements. But how do we know which requirements are the right ones? How do we choose which requirements to spend time on and which ones to put in the waiting room? And how can we determine whether we're missing any of the "right" requirements? The answer to all these questions lies in having a well-understood reason for doing the project along with quantified expectations of its costs and benefits. We often refer to this collection of knowledge as the business case. A business case provides a mechanism for justifying and guiding a project. The business case is the basis for deciding the most profitable investment of effort. It's the project driver.