Philosophically speaking, how can "I don't know" be a wrong answer?
I looked right through the correct answer in the documentation (not enough coffee yet) so I clicked the answer that was appropriate and yet still got it wrong. I didn't know so the correct answer was "I don't know" but that wasn't right but I didn't know so it had to be right and now I'm just glad it's Friday.
On two occasions I have been asked, "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" ... I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
—Charles Babbage, Passages from the Life of a Philosopher
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