Answer:
Mathilde has been endowed with physical beauty, but she has not been rewarded with the rich lifestyle that she desires, and she is very dissatisfied with her position in life, as seen in the film. After borrowing a diamond necklace from her friend Madame Forestier in order to attend a lavish party, she loses the necklace and is forced to labor for ten years in order to pay for a replacement. Her one night of brilliance ended up costing her and Monsieur Loisel all hope of a future happily ever after together.