Early in the story, Tom's wife leaves for the movie theater. Tom has already opened a window because he thought the apartment felt too warm. When he opens the door into the hallway for Clare to leave, a cross-draft blows from the hallway through his living room and, before he can get the door shut, the draft has started scattering the papers on his desk. (Later, when he is outside looking through his window, we realize that he has placed his desk within two feet of the window, probably to get the best light in the daytime as well as to enjoy the view while he works there.
The sheet of yellow paper which is so precious to him behaves in a perverse way, almost as if it had a soul of its own. First, it plasters itself against the window pane and the bottom of the wooden window-frame.
Then as the moving air stilled completely, the curtains swinging back from the wall to hang free again, he saw the yellow sheet drop to the window ledge and slide over out of sight.
This seems a little uncanny--both to Tom and the reader. Inanimate objects often seem to act perversely. The paper seems to be playing cat-and-mouse with him. When he looks out the window he sees that the paper hasn't blown off into the air like a kite; instead--as if to tease and torment him--it has plastered itself against the wall only about five yards away.
It just happens that there is a narrow ornamental ledge right outside his window. The situation is tempting enough to lure Tom out the window in pursuit of the yellow sheet of paper which has cost him so much time and brain work.
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, gone over page by page in snatched half-hours at work and during evenings at home, 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 lend authority to his idea for a new grocery-store display method; without them his idea was a mere opinion.
If Tom hadn't decided to stay at home instead of going to the movies with his wife, he wouldn't have opened the window. In that case there would have been no draft from the hallway to make his memo sheet slide out the window onto the ledge. A connected series of events led to Tom's finding himself out on the ledge eleven stories above the street, paralyzed with fear and realizing that what he was doing was crazy. It was his blind ambition that was making him crazy, and now he was recovering his sanity when it might be too late.