I made a little sticky note for someone I manage, but I don’t have a scanner here.  So I recreated it for you.

It’s amazing to me how often people break this rule. Everyone thinks the other person knows what they are talking about.  People are happy to pass the buck and add features or functionality that they have no idea why someone would use it.  It’s not enough to know HOW it works.  You have to understand what is happening in the user’s head.  Ask “Why would they be interested in doing this?”  Often you might realize that only a tiny fraction of users actually are interested.

If you are a designer or an engineer, you shouldn’t just take the other person’s word for it.  Really understand the motivation of the user and you will build the product better.  I promise.  Take my word for it.