Mathilde Loisel was born into a middle class family of clerks, but felt as if she should be rich and famous.
Her husband gives her a fancy invitation to an elegant party, but weeps because she doesn't have anything to wear.
Her husband gives her money for a dress, but she absolutely needs jewelry. She ended up borrowing a diamond necklace from her wealthy friend.
She parties the night away all night until morning. When she takes a cab back to her house she immediately sulks of not having all those fancy things.
As soon as she walked in, she notices the diamond necklace is gone! Her and her husband loan tons of money to replace the necklace and are deep in debt.
10 years later, the debt was paid off, but they were still poor. She ran into her friend that had loaned her the necklace, years ago, and told her the story. Turns out the "diamond" necklace was fake...