The Merriam Webster Online Dictionary defines the term "MacGuffin" as follows:
: an object, event, or character in a film or story that serves to set and keep the plot in motion despite usually lacking intrinsic importance.
For example, the MacGuffin in Dashiell Hammett's novel The Maltese Falcon, as well as in the film version, is the statuette of a black bird. In Jack Finney's "Contents of the Dead Man's Pocket," the author takes pains to establish the value of a single sheet of yellow paper to the protagonist Tom Benecke. Although this is nothing but a sheet of paper, it is of immense value to him because he has spent so many hours jotting notes on it. The plot of Finney's story is very simple. The paper blows out the window, and Tom wants to retrieve it; he wants it badly enough to risk his life for it.
Of all the papers on his desk, why did it have to be this one in particular! On four long Saturday afternoons he had stood in supermarkets counting the people who passed certain displays, and the results were scribbled on that yellow sheet. From stacks of trade publications...he had copied facts, quotations, and figures onto that sheet. And he had carried it with him to the Public Library on Fifth Avenue, where he'd spent a dozen lunch hours and early evenings adding more. All were needed to support and led authority to his idea for a new grocery-story display method; without them his idea was a mere opinion. And there they all lay in his own improvised shorthand--countless hours of work--out there on the ledge.
The author needed to justify to the reader how it could come about that a sane married man would find himself on an extremely narrow ledge eleven stories above the street. The most important setting, of course, is the ledge on the outside of the building. Finney spends five paragraphs describing Tom's reservations about climbing out his window, beginning with the following sentence:
For many seconds he believed he was going to abandon the yellow sheet, that there was nothing else to do.
But he finally talks himself into it. By this point the reader is fully identified with Tom and is out there on the ledge with him, hugging the brick wall and inching along towards that precious sheet of paper. The reader identifies with the protagonist because he or she is kept in that one point of view and because the reader has come to appreciate the MacGuffin's great value.
It is a common plot device in commercial stories such as "Contents of the Dead Man's Pocket" to get the protagonist in a dangerous situation--and then make it even worse. Even the title chosen for the story seems to suggest that Tom is going to lose his life because he made the foolish mistake of climbing out on a ledge which is not even as wide as his foot. He knows enough not to look down. He keeps one side of his face pressed against the bricks and holds on to the spaces between them with his fingertips.
But then when he gets to the paper he is forced to look down. Finney has saved the sight to create an emotional climax. His one-paragraph description of Manhattan from eleven stories up is excellent. He must have worked on it for a long time. It begins:
He saw, in that instant, the Loew's theater sign, blocks ahead past Fiftieth Street; the miles of traffic signals, all green now; the lights of cars and street lamps; countless neon signs; and the moving black dots of people. And a violent instantaneous explosion of absolute terror roared through him.