Perfection is the enemy of progress. When do you quit polishing, call it “good enough” in order to ship or validate it?
”When designing use cases too often the end game scenario is used as a reference.”
Such an end game scenario is an alluring vision or target to aim for, but a bloated MVP. What elements are needed for the next step, the iteration you are seeking to make. What are the elements that when present and working, will convince the stakeholders of your project? What will make them comfortable enough to go ahead with the next step?
Rome was not built in a day. You would do harm to your vision if you rush to the end game and skip a number of critical lessons along the way.
Need help scoping your use case and making sure your End Game does not cloud your MVP?