The natural mistake engineers make is to build from the bottom up. They leave the user interface last, assuming it is the least complex technology. This is wrong. Humans are much more complex than software, and since the interface has to interact with people, it's the most difficult to do well. By building from the bottom up, technologists paint themselves into a corner, resulting in ugly, hard-to-use things. By the time they finally got to the user interface work, so many constraints exist that even the best designers in the world couldn't salvage the project.
