What is the theme of "The Necklace"?

One possible theme of "The Necklace" can be the idea of being unhappy with what you have. Madame Loisel is unhappy with her lot in life. Feeling as if she is "born for every delicacy and luxury," Madame Loisel "suffers" from a lack of what she feels she is entitled to. She longs for jewelry and beautiful clothes, for "these were the only things she loved."
Madame Loisel's unhappiness and sense of entitlement become apparent when her husband comes home with an invitation to a fancy affair. Instead of being excited and happy, she tosses the invitation aside. She complains that she has nothing to wear, so he suggests that she spend some money on a dress. Once she purchases the dress, she complains because she doesn't have suitable jewelry. Taking her husband's suggestion to borrow a necklace, she does just that. However, after returning home and realizing she has lost the necklace, her life changes. If she had been happy with what she had, she would not be in the predicament she finds herself in near the end of the story.