Mark Twain famously said, "Denial ain't just a river in Egypt." But this is something we must deny. First off, Denial is not a river in Egypt. Perhaps he had it confused with the Nile, which is a river, or else the Sebennytic, which is another river in Egypt, although not as famous. But on top of that, Mark Twain never said that, although the quotation is famous precisely because he did say it, because Twain knew too much about Egyptian rivers to make a careless error like that with their names. He's more likely to have said, "Romance ain't just a city in Arkansas," because whereas Romance really is a city in Arkansas, there is no such river as Denial, as far as I can tell.
So we can deny that Mark Twain said, "Romance ain't just a city in Arkansas," but we can't deny that it actually is, but we can deny that Mark Twain ever said, "Denial ain't just a river in Egypt," as well as that there really is a river in Egypt named Denial or ever was one.
And yet people still deny it.