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"
http://www.eyecons.com/how%20to/icons.htm
"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)
http://doctoryourself.com/motivate.html
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