Blue Mountain
Resident Skeptical Hobbit
You wouldn't expect a carpenter to not know how to use a circular saw, but you also wouldn't expect them to understand the internal electrical circuitry that makes it work.
Surely the general principle is that a tool is something that I can competently use but can't necessarily make.
Sure, that's a reasonable definition. I would also say that it's possible to be able to competently use a tool without understanding how or why it works the way it does.
As far as the "tool" part goes, I think we can safely assume that for modern office work computers are tools users should be familiar with. If the job you're doing requires a spreadsheet, word processor, presentation software, CAD, etc, I'm of the opinion people should either know how to use them or be willing to learn.
So where does this leave the user in Accounting who needs help resizing a column in Excel? Do I sigh, show them, and hope they remember it? And if I see too much of that, take it up with their supervisor? Or do I go all JoeMorgue on them and tell them to do their own bloody learning because I'm not their teacher?
For me, it's the first option. At least the first time. If users made a habit of it I'd be inclined to show them where they can find the answers themselves, and failing that kick the problem upstairs:
User's supervisor: "So why are you telling me this?"
Me: "Up to now, it's been a problem between me and the user. Now that I've informed you, it's your problem."