The rationale is the reason, or justification, for a requirement. We have found that attaching a rationale to the requirement makes it far easier to understand the real need. Quite often, stakeholders may tell you their perceived solution to the problem, rather than their real need. Alternatively, they may state a requirement that is so vague as to be (for the moment) unusable. In the example given previously, the client asked for a “user-friendly” product, but you could make sense of it when you learned that the rationale was that the project needed the users to readily adopt the product.
Link · 12. Fit Criteria and Rationale