Customer First Design

I came across this article on the birth of Amazon EC2. Buried in the middle is this gem:

…in the amazon style of "starting from the customer and working backwards", we produced a "press release" and a FAQ to further detail the how and why of what would become EC2.

Before one mockup, diagram, line of code, or anything had been done, they wrote the FAQ and the press release. Customer first design makes things very black and white during a dev cycle.