Experienced object designers explore the design space from many different angles. They refine ideas of how their system should respond while they are in the middle of building and discarding ideas about how their design should work. Getting a design to gel involves making assumptions, seeing how they play out, changing one's mind or perspective slightly and re-iterating. Design is a difficult, involved task. It inherently is a non-linear process. Yet, we are asked to trace our design results back to system requirements. And, if we uncover some implications during design, we'd like to tune our system requirements to reflect necessary design compromises.

Abstract - Designing scenarios: Making the case for a use case framework (1993)