There’s always one
It doesn’t matter if you’ve been telling everyone for three days that there is a problem.
It doesn’t matter if you’ve posted a message on the front page of the intranet telling people what the problem is and how to fix it.
It doesn’t matter if you’ve circulated the fix to the entire staff by email.
There’s always someone who will wander into your office with a puzzled look on their face and ask, “Why isn’t this thing working?”