Perhaps the author was paraphrasing? Or if it was said by a character, perhaps it was meant to be written "wrong". Or perhaps the author AND the editor seriously didn't know the difference.
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Famous Phrases You Have Been Misquoting
Quoting famous authors or thinkers is presumably a reflection of one’s erudition. But what it does it say about the speaker, if they don’t even know that the quotation they are using is…