The cure reminds me of what Fred Brooks said in The Mythical Man-Month after 20 years, at p.258-9 (MM-M, 2nd ed.) about defining the user set (ie. who the users are), as a population assessed along several attributes, with a frequency distribution over each (my eg. how much RAM they have; their largest file - but the most interesting ones are app-specific). He says you should GUESS the set of attributes and distributions:
1. you will think about it carefully;
2. they will be debated by the team, revealing differences in how each member sees the user set;
3. it "helps everyone recognize which decisions depend upon which user set properties. Even this sort of informal sensitivity analysis is valuable. When it develops that very important decisions are hinging on some particular guess, then it is worth the cost to establish better estimates for that value."
He summarizes: "It is far better to be explicit and wrong than to be vague"