The designers thought they knew who would be using the interface and how much experience they had with interfaces like this, and they designed accord- ing to those assumptions without testing them, and it turns out their assumptions were wrong.

The audience or the product or Web site is varied. The designers designed for one persona or type of audience, and the mental model and conceptual model match for that group, but not for others.

There are no real designers. The conceptual model wasn’t really designed at all. It’s just a reflection of the underlying hardware or software or database, so the only people whose mental model it fits are the programmers. If the audience is not the programmers, then you’re in trouble.

32. People Interact With Conceptual Models