The Internet isn't much help on this one, sorry to say...
Most of the attributions I saw went to Rogers.
To paraphrase Will Rogers, "It ain't so much what we don't know that gets us into trouble as what we do know that ain't so"
"It's not what we don't know that harms us;
it's what we do know that ain't so."
~ (Attributed to Eubie Blake)
and then there is the obligatory attribution to...
Mark Twain once opined that it's not so much what we don't know that hurts us; it's what we do know that ain't so!
http://www.trinidadco.com/stories99/new ... reamy.html