There's a door at work with a label next to it that reads, in half-inch-high capital letters: "DON'T PULL THE DOOR UNTIL IT CLICKS."
Now, first of all, as I'm sure Donald Norman would tell us: if the interface for a door is so confusing that it needs to be documented, then it's probably not a very good UI.
But, okay, in this case we probably can't fix the UI. But if we have to provide documentation for a simple interface, we should at least provide good documentation.
The abovequoted label is ambiguous to the point of being confusing, at least to me. It's trying to tell us what not to do, but it hasn't made clear which aspect of the proscription is the relevant one.
Is the problem that a lot of people come by here and pull the door until it clicks (whatever that means), and that's bad for some reason? That was, honestly, what I thought the label meant at first glance.
In fact, the idea is that to open the door, you put your badge near the magnetic badge reader, and a second or two later the door unlocks with a loud click, and until the door is unlocked, pulling on it won't have any effect, except (probably) to annoy the people in the offices right next to the door. It's possible that if you're pulling on it at the exact moment of unlocking, that'll result in any of various problems, too; that happens with some doors.
So what the labelmaker really meant to say was: "Wait until the door clicks before you try to open it."
And in fact, what I haven't told you is that there's another label, on the door handle itself, that says: "WAIT UNTIL DOOR CLICKS."
Which makes more sense and is more concise. But it's placed in such a way that I always see the other one first.