Ray Kim has a good reminder for us:
I spoke to the form’s owner (this is where the political part comes in). I explained what I was doing. However, he keeps insisting: “it doesn’t have to be documented, because the form is the documentation.”
He showed me a screen shot of text on the form that explains how the particular request works. The text made a lot of sense, and it would have been ideal to fulfill at least part (if not most) of my needs. I decided that I would create a reference to it. So I looked around the form for it… and could not find it anywhere.
He finally told me that “you had to click a specific button on the form to view the text.”
If you’ve developed a process or product, it’s easy to forget that you have a fuller mental model than anybody else, and so things which are blindingly obvious to you probably aren’t to users.