This is an excerpt from Robert Heinlein's "Gulf":

"If the average man thinks at all, he does silly things like generalizing from a single datum. He uses one-valued logics. If he is exceptionally bright, he may use two-valued, 'either-or' logic to arrive at his wrong answers. If he is hungry, hurt, or personally interested in the answer, he can't use any sort of logic and will discard an observed fact as blithely as he will stake his life on a piece of wishful thinking. He uses the technical miracles created by superior men without wonder nor surprise, as a kitten accepts a bowl of milk. Far from aspiring to higher reasoning, he is not even aware that higher reasoning exists. He classes his own mental proccess as being of the same sort as the genius of an Einstein. Man is not a rational animal; he is a rationalizing animal.

For explanations of a universe that confuses him he seizes onto numerology, astrology, histerical religions, and other fancy ways to go crazy. Having accepted such glorified nonsense, facts make no impression on him, even at the cost of his own life. Joe, one of the hardest things to believe is the abismal depth of human stupidity.

That is why there is always room at the top, why a man with just a little more on the ball can so easily become governor, millionaire, or college president - and why homo sap is sure to be displaced by New Man, because there is so much room for improvement and evolution never stops.

Here and there among ordinary men there is a rare individual who really thinks, can and does use logic in at least one field - he's often as stupid as the rest outside his study or laboratory - but he can think, if he's not disturbed or sick or frightened. This rare individual is responsible for all the progress made by the race; the others reluctantly adopt his results. Much as the ordinary man distrusts and persecutes the process of thinking he is forced to accept the results occasionally, because thinking is efficient compared with his own mauderings. He may still plant his corn in the dark of the Moon but he will plant better corn developed by better men than he.

Still rarer is the man who thinks habitually, who applies reason, rather than habit pattern, to all his activity. Unless he masques himself, his is a dangerous life; he is regarded as queer, untrustworthy, subversive of public morals; he is a pink monkey among brown monkeys - a fatal mistake. Unless the pink monkey can brown himself before he is caught.

The brown monkey's instinct to kill is correct; such men are dangerous to all monkey customs.

Rarest of all is the man who can and does reason at all times, quickly, accurately, inclusively, despite hope or fear or bodily distress, without egocentric bias or thalamic disturbance, with correct memory, with clear distinction between fact, assumption, and non-fact. Such men exist, Joe; they are 'New Man' - human in all respects, indistinguishable in appearance or under the scalpel from homo sap, yet as unlike him in action as the Sun is unlike a single candle."