This was one of the key points drilled at the Shelter Training Course I attended last weekend. A quote I happened to stumble upon today to demonstrate the point:
"Jabe Blumenthal liked to ask program manager candidates [during interview] to design a house. Sometimes the candidate would go to the white board and draw a square.
This is about the worst possible thing to do, in Blumenthal's estimation. A house can be anything. You never build a house without asking who's paying for it and how much money, space, and time are available...
... One of Blumenthal's collegues, Joel Spolsky, took to interrupting the square-drawers. 'Actually, you fogot to ask this,' he'd say, as they were putting the finishing touches on their floor plan, 'but this is a house for a family of forty-eight-foot-tall blind giraffes'."
(Source: How Would You Move Mount Fuji?, Microsoft's Cult of the Puzzle, How the World's Smartest Companies Select the Most Creative Thinkers)