My basic assumption is that people aren't stupid but they *can*
   get locked into a mode of thinking. This can affect anybody,
   from a child that refuses to eat french fries because they were
   scared by a clown while eating french fries once, or an
   intellectual well versed in a variety of world issues.

   I've worked with people of all ages and "intelligence levels"
   and while I have seen thick-headedness (even in myself), I
   haven't found genuine intelligence differences between people.

   Language barriers? Certainly. Comprehension difficulties?
   Definitely.

   But I've found little that can't be explained to anybody given
   the right metaphors/analogies/explanations.