Mathilde spent her entire life wanting to be socially important, wealthy, own many luxurious possessions, and desired. While she was a beautiful woman with a loving husband, she felt she deserved better than her middle class lifestyle.
In an attempt to make his wife happy, Mathilde's husband secures invitations to an exclusive ball. He knows that their average lifestyle is not to her liking, and is making an effort to fulfill her desire to be among the wealthy. After much drama, Mathilde is suitably attired and drenches herself in a beautiful diamond necklace that she has borrowed.
During the ball, Mathilde feels that she is finally in her true element. She has a grand time, but it ends all too soon. On this particular night, Mathilde feels she has finally found happiness. The superficiality of her happiness is not evident to Mathilde at this point. To her horror, she has lost the necklace.
To replace the necklace, she must work herself into exhaustion. Her previous good looks have vanished in all the toil, and her ability to appreciate any small pleasure is gone. Her momentary pleasure in a night of social pleasantries costs her everything.
To make matters worse, she learns the necklace she borrowed was a fake. Mathilde learned that a superficial desire cost her her youth, vitality, and beauty.