Go to the bookstore and look at how many bookshelves are filled with books trying to explain how to work the devices. We don't see shelves of books o… - Donald Norman

The principle of visibility is violated over and over again in everyday things. In numerous designs crucial parts are carefully hidden away. Handles on cabinets distract from some design aesthetics, and so they are deliberately made invisible or left out. The cracks that signify the existence of a door can also distract from the pure lines of the design, so these significant cues are also minimized or eliminated. The result can be a smooth expanse of gleaming material, with no sign of doors or drawers, let alone of how those doors and drawers might be operated.

When I use a direct manipulation system—whether for text editing, drawing pictures, or creating and playing games—I do think of myself not as using a computer but as doing the particular task. The computer is, in effect, invisible. The point cannot be overstressed: make the computer system invisible.

Technologists are not noted for learning from the errors of the past. They look forward, not behind, so they repeat the same problems over and over again. [...] As each new technology matures, customers are no longer happy with the flashy promises of the technology but instead demand understandable and workable designs. Slowly the manufacturers relearn the same basic principles and apply them to their products. The most egregious failures always come from the developers of the most recent technologies.