in reply to
When writing code for end users, what operator error surprises you the most?
Perhaps "surprises" isn't the right term. I have stopped being surprised by users' inability to read instructions. Nor am I surprised that for so many, it never occurs to them that they could read the instructions. I am amazed by this blind spot, which often extends to an inability to read whatever error message is displayed in front of them, but I am no longer surprised by it. It's sad, really.
"What do I want? I'm an American. I want more."