By Mark Twain
From The Comedy of Those Extraordinary Twins (1893-1894).
As you see, it was an extravagant sort of a tale, and had no purpose but to exhibit that monstrous "freak " in all sorts of grotesque lights. But when Roxy wandered into the tale she had to be furnished with something to do; so she changed the children in the cradle: this necessitated the invention of a reason for it;
this in turn resulted in making the children prominent personages -- nothing could prevent it, of course. Their career began to take a tragic aspect, and some one had to be brought in to help work the machinery; so Pudd'nhead Wilson was introduced and taken on trial. By this time the whole show was being run by the new people and in their interest, and the original show was become side-tracked and forgotten; the twin-monster and the heroine and the lads and the old ladies had dwindled to inconsequentialities and were merely in the way. Their story was one story, the new people's story was another story, and there was no connection between them, no interdependence, no kinship. It is not practicable or rational to try to tell two stories at the same time; so I dug out the farce and left the tragedy.
The reader already knew how the expert works; he knows now how the other kind do it.