“And most important, expect the best answer to change.”
This entire post strikes me as how Apple does things. John Gruber has written about what Apple does with their products once they are released; but I think this is what Apple does before their products are released. They make prototypes, physically, to see how they work under actual situations. Nothing theoretical or etherial, no checklists, no fancy CGI with the average human hand modeled on a computer screen. Just a near finished product to test in real world scenarios. Then they make it better.