It is a popular fact that nine-tenths of the brain is not used and, like most popular facts, it is wrong. Not even the most stupid Creator would go to the trouble of making the human head carry around several pounds of unnecessary gray goo if its only real purpose was, for example, to serve as a delicacy for certain remote tribesman in unexplored valleys. It is used. And one of its functions is to make the miraculous seem ordinary and turn the unusual into the usual. Because if this was not the case, then human beings, faced with the daily wondrousness of everything, would go around wearing big stupid grins.
-Terry Pratchett, Small Gods