The Product Usability Web log has a good article talking about the gap between what the designer knows and the user is capable of in the design of applications.

The designer-user gap

This is what Jakob Nielsen (or his ghostwriter) in his Alertbox column is calls the designer-user gap. Nielsen identifies three levels of designer-user gaps:

• Level 1: The Designer Is the User (he completely understands how the product works, and so do the users)
• Level 2: The Designer Understands the Product (and the designer is in the dangerous position of knowing more than the user group)
• Level 3: Designing for a Foreign Domain (where the designer has the problem that he knows much less than the user group)

The reality is that we are almost never the target audience, so when we say that to some executive that wants it red or blue, the truth is that they may be closer to the target audience than we are.