You can read "The Necklace" as a story about greed, but you can also read it as a story about pride. Mathilde Loisel is a proud woman. She feels far above the humble circumstances (and the husband) she's forced to live with by her common birth. In fact, her current situation disgusts her. She's a vain one too, completely caught up in her own beauty. It could be that it is also pride that prevents Mathilde and her husband from admitting they've lost an expensive necklace. After the loss of the necklace makes Mathilde poor, and her beauty fades, she may learn a pride of a different sort: pride in her own work and endurance.
It's M. Loisel's pride that is responsible for the tragedy at the end of the story.
It is not pride, but the Loisels' sense of honor, which is responsible for the tragedy at the end of the story.