And it occurred to him then with all the force of a revelation that, if he fell, all he was ever going to have out of life he would then, abruptly, have had. Nothing ... could ever be added to his life. ... He thought wonderingly of his fierce ambition ... he thought of the hours he'd spent by himself, filling the yellow sheet that had brought him out here. Contents of the dead man's pockets, he thought with sudden fierce anger, a wasted life.
This is the same question Tom poses to himself in the quoted text above: what was it for? The quote tells us clearly the answer: it was for Tom's "fierce ambition." Let's examine how this ambition is revealed so we can see what Tom sees so clearly finally. The introduction in the exposition of Tom's conflict will help us understand Tom's answer.
When Tom helps Clare on with her coat and smells her perfume, through the closely proximal or near narrator, Tom confesses that "it was not actually true that he had to work tonight." Tom, through indirect dialogue provided by the narrator, explains that though he doesn't have to, he very much wants to work because the Interoffice Memo he wants to type explains and lays out the details of an independent project he has been laboriously collecting data for. He wants to get the data typed up to present to his boss next day for reading over the weekend.
This demonstrates for us that Tom's ambition leads him to take initiative, devote personal time to research, and give up his personal life of comfort to pursue a long-term plan for advancement in his career (pursuing such a plan, in itself, is not an error). This explanation is the first, small picture we are given of Tom's driving ambition and the first introduction of the internal conflict of ambition versus personal happiness.
You can examine the text for other instances that shed light on the answer Tom gives. Examine the portion of text when he is out on the ledge and sees Loew's theater, then analyze its connection to Clare. Analyze the few lines Clare speaks, then see what other word can be spelled from the letters in her name. Examine the flashback narrated while Tom is staring out the window at the lost paper on the ledge when he thinks about how he accumulated the contents of the yellow sheet of paper. These and other textual instances you can find will draw a strong picture of Tom's fierce ambition and reveal how ambition drove him out onto the ledge.
For many seconds he believed he was going to abandon the yellow sheet, that there was nothing else to do. ... [His independent projects] were the beginning of the long, long climb to where he was determined to be, at the very top. And he knew he was going out there in the darkness, after the yellow sheet fifteen feet beyond his reach.
It may seem crazy for a man to climb out of his window onto a narrow ledge eleven floors above the street in order to retrieve a single sheet of paper. This was a problem that the author Jack Finney had to wrestle with in order to get his reader involved with his story. Finney takes great pains to explain how valuable that sheet of paper is to his hero Tom Benecke. He was all set to write his report. That was why he was staying home rather than going to the movie with his wife. The story opens with a sentence which shows that he has reached his moment of truth.
At the little living-room desk Tom Benecke rolled two sheets of flimsy and a heavier top sheet, carbon paper sandwiched between them, into his portable.
He is already thinking about what he is going to put into that interoffice memo. But the facts and figures are not in his head. They are all on the sheet of paper which, with the notorious perversity of inanimate objects, chooses to take flight and escape out the window.
It was hard for him to understand that he actually had to abandon it--it was ridiculous--and he began to curse. 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, 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. And there they all lay in his own improvised shorthand--countless hours of work--out there on the ledge.
It should be noted that his findings were written "in his own improvised shorthand." The author adds this information because it serves to make the yellow sheet that much more valuable. Since everything is written in shorthand, the paper actually contains the equivalent of several sheets of handwriting. The information is all compressed. If written down in conventional prose it would have to take up more than one sheet. But if it were all written out in conventional prose rather than shorthand, it probably wouldn't be able to take flight the way it did.
Jack Finney spends several paragraphs describing the struggle that goes on in his protagonist's mind over whether to abandon the paper or whether to try to retrieve it. This is good writing. The reader would be less likely to identify with Tom Benecke if Tom simply decided to climb out the window and crawl along the ledge. Tom, like the reader, knows it is dangerous; but the reader is finally convinced that Tom made the correct decision, because the reader finds himself, in his imagination, out there on the ledge with Tom. If the reader were not convinced, he might stop reading the story altogether.
Everyone is familiar with the feelings created by being up on a great height. Some people have a phobia that prevents them from going even as high as the second floor of a building. It is very easy to identify with Tom, especially since we are confined to his point of view from beginning to end. We suffer his terror and his paralysis. We experience his epiphany when we realize that life itself is more precious than any hypothetical reward. The story is successful because the author succeeds in persuading the reader that Tom's decision to risk his life was plausible, even though it turned out to be a bad mistake.
Tom Benecke risks his life because he believes that paper is worth it. He believes that that paper will make him earn more money and make him happy. He isn't worried about going out with his wife, he would rather choose work.