Characteristically, Guy de Maupassant plays ironically upon the words singular and small in these lines, for one of his major concerns in his writing is the pettiness of the bourgeoisie of his native Normandy as in "The Necklace" and "The Piece of String." For, it is the singular (as in particular to her, and odd) pettiness (smallness) of Mme. Loisel which becomes her nemesis. Were Madame Loisel content to go without a necklace to the party, the night could not have taken the turn that it has. If she were forthright in admitting to her friend that she has lost the necklance, Mathilde Loisel could not suffer as she has.
That Mme. Loisel is tragic in her defiant pettiness is evidenced in her encounter with her old school friend in the denouement of the story. For, with her characteristic pettiness, she announces to Mme Forestier how much she has sacrificed and suffered
"plenty of misfortunes--and all on account of you!"
And, with a perverse pride, also, she announces that she has paid Mme. Forestier back without her noticing that the necklace was different. And, here the singular irony presents itself to Mme. Loisel because of her pettiness:
"But mine was only paste."
Indeed, "how small a thing--pettiness and a paste necklace--can ruin one.