I’ve always been constantly surprised more interaction and UX designers don’t think in these terms.
I took this picture of a door in my office. It has two handles. The top large green one is for emergencies only, and people have apparently been using it. To solve the problem, a large sign has been taped to the handle bearing the legend:
“Do not use this door handle unless it’s emergency situation”
Problem solved. Anyone can see that there’s something wrong here. But let’s boil it down:
The handle problem
If the handle is not to be used, placing it above the normal handle, making it larger and green is probably a bad idea. In fact, it’s the exact opposite of what you’re supposed to do according to various studies on cognitive processes, visual recognition and psychology. Of course, this design is made for emergencies only and for such is pretty good.
The normal handle below the emergancy handle requires the user to touch a button on the wall first in order to open the door. The additional step of course makes it less useable, but the really interesting design choice here is WHY THE F why in the world one of the handles require a button on the wall and the other does not… The result is the same so there is no difference to the user. Couldn’t the second handle also be used by just, you know, pushing it? And while we’re at it, why not just have one handle from the start? It would be much more cost effective.
The sign problem
The sign is another great feat of design. First of all it obscures the handle. Rendering it useless in an emergency situation. But since the sign is well fastened and laminated with hard plastic you wouldn’t be able to use it even if you knew where it was.
Smart people were involved in every step of this process. But noone looked at the overall intended function, nor the users intended use. Not one. This is why you need designers.