There was an artist who worked for the prince of Qi.
"Tell me," said the prince, "What are the hardest things to paint?"
"Dogs, horses, and the like," replied the artist.
"What are the easiest?" asked the prince.
"Ghosts and monsters," the artist told him. "We all know dogs and horses and see them every day; but it is hard to make an exact likeness of them. That is why they are difficult subjects. But ghosts and monsters have no definite form, and no one has ever seen them; so they are easy to paint."
Han Fei Zi