Green Threads was an early precursor to many of the outside-in design principles we see in IBM today. It captured user design scenarios across a set of products that solve a customer problem. It moved out organization beyond product thinking.
A scenario is a key artefact in our design. It ties together the personas and their objectives with their workflows and pain-points. It forms the basis we derive solution requirements, like release hills. And the way we validate our design using playbacks.