TT: Almanac

"If you say that two sheep added to two sheep make four sheep, your audience will accept it patiently--like sheep. But if you say it of two monkeys, or two kangaroos, or two sea-green grifins, people will refuse to believe that two and two make four. They seem to imagine that you must have made up the arithmetic, just as you have made up the illustration of the arithmetic. And though they would actually know that what you say is sense, if they thought about it sensibly, they cannot believe that anything decorated by an incidental joke can be sensible. Perhaps it explains why so many successful men are so dull--or why so many dull men are successful."

G.K. Chesterton, Autobiography