If you're not familiar with the Sandman, he's neither Steve Abbott nor a benign dust-sprinkling imp. Gaiman's Sandman is Morpheus, Lord of Dreams, one of the family called the Endless. His brother is Destiny, his sisters are Despair, Delirium and Death, and Desire is brother, sister, both and neither. And, although Morpheus is a romantic figure, you really wouldn't want him to visit you if you're having problems sleeping.
Anyway, before I started the story, I read Harlan Ellison's introduction. Ellison is acerbic and incisive and very funny at times. In his introduction to Seasons of Mists, he careers from point to point like a pinball until he cannons into the conclusion. But before he get there, he makes a number of astute comments on writing. Here's his observation on the 'what if' of story-telling. He's referring to speculative fiction but it applies to all novels. After all, even the slice-of-life, mimetic works take place in non-existent worlds.
... every fantasist builds a new universe each time s/he creates a new story. It's the way the game of "what-if?" is played. Some people do it better than others; and most people can't do it at all (which is why there are folks who believe that actors make up their own lines, that truth is stranger than fiction, that one picture is worth a thousand words, and that we are regularly visited by far-travelling malevolent incredibly intelligent aliens in revolving crockery, who have nothing better to do with their time than snag couch potato humans so they can have unfulfilling sex with them and just for laughs give these lousy sex partners rectal examinations with mechanical appendages the size of oil pipeline caissons); and every once in a while a person does it so splendidly that it raises the high water mark and puts more sunlight in the world.
Ain't that the truth.