Aza’s Thoughts » Write the manual first.
http://www.azarask.in/blog/post/write-the-manual-first
"You don’t really know a subject until you’ve had to teach it. In the same way, you don’t really understand your interface until you’ve written a manual explaining how to use it. It can be a frustrating experience. Take for example the two manuals for digital watch and analog watch. The section on setting a digital watch is over a page of dense, difficult explanation. The analog’s is a single sentence: “Pull crown and turn.”"