It's not just a question of IQ (three standard deviations above the mean in my case); or trained thinking - rationality has been more or less "instinctive" for me since early childhood.
I think the point is most folks, smart or not, are intellectually lazy and dishonest. If you are looking for short-cuts in thinking and not too scrupulous about what is actually the truth of the matter, sure you're going to make mistakes in your thinking.
This isn't the sort of person you'd want to have as a lab partner in Physics class. :)