Irony doesn't come much easier than this. Saturday's New York Times featured an article on "The Overconfidence Problem in Forecasting," about the almost universal tendency for people to think their assessments and decisions are more correct than they really are. The article closes smartly with this quote from Mark Twain:
“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”
Very tidy. Except there's no good evidence that Mark Twain ever wrote or said those words. (And neither did humorist Will Rogers.)
The actual author? It may be Charles Dudley Warner, an editorial writer for the Hartford Courant who was a friend of Mark Twain and who might have been paraphrasing him... or someone else... unless he was simply piping an imaginary quote for better copy. We may never know.
Bob Kalsey examined the roots of these fatherless words in 2008, and pointed out that similar sentiments were voiced by Confucius, Socrates and Satchel Paige, among others.