When the young man flings himself upon the park bench next to Norman Gortsby, the man who counts himself among "the defeated," Gortsby is apparently not fooled by the youth's story of having gone out to purchase soap and then forgotten at which hotel he is staying. For, as he first relates his tale of woe, Gortsby is quickly wary. However, after giving no credibility to the young man's tale of having lost his way and not remembering his hotel, because of a credibility gap in the story, Gortsby tells the youth,
"Of course," said Gortsby slowly, "the weak point of your story is that you can't produce the soap."
After the young man searches in his pockets and "mutters angrily" that he must have lost it, he rushes off. But, as chance would have it, there on the ground beneath where the young man has sat is a bar of soap.
Lying on the ground by the side of the bench was a small oval packet, wrapped and sealed with the solicitude of a chemist's counter....[that] had evidently fallen out of the youth's overcoat pocket when he flung himself down on the seat.
With the chance circumstance of the soap being on the ground beneath the bench where the youth has been sitting, Gortsby is fooled, and he incorrectly deduces that the youth has justifiably been angry when not believed. So, he seeks the young man and provides him with a loan of money. The "catch in his voice" of the young man's is not the youth's restraint from breaking down, either. Instead, it is the youth's surprise at his good fortune when Gortsby mistakenly assumes the soap is his.
The young man's story was cleverly constructed and carefully rehearsed. The fact that he couldn't produce the cake of soap to substantiate it was his one mistake. There is one especially clever element in the hard-luck story which has not been pointed out in previous answers. In Gortsby's time it was not customary for hotel guests to pay in advance. They would settle up with the desk clerk when they were checking out. But this was true only when the guests had luggage. The young man has concocted a story which explains why he probably has plenty of luggage but doesn't have access to it. The logical thing for someone in his situation to do, if he were honest, would not be to approach total strangers on park benches but to go to various hotels in the vicinity and ask to be accommodated overnight without paying in advance. The hotel clerks would be quite used to renting rooms without expecting advance payment. The only exception they would be asked to make would be to overlook the fact that the young man didn't have any luggage. Luggage served as insurance that a guest could not leave without settling up for the rent. It would seem to be easier for a presentable and well-spoken young man to get a hotel clerk to trust him overnight than to get some stranger like Gortsby to give him money so that he could pay his hotel rent in advance. This apparently doesn't occur to Gortsby, but it is a better clue to the young con man's fraudulent intentions than the fact that he doesn't have the cake of soap he supposedly went out to buy.