Irony is a very effective device in literature and exists in two forms. Verbal irony is a method in which "statements often convey a meaning exactly opposite from their literal meanings." In situational irony, which is what gives "The Necklace" by Guy de Maupassant its stunning twist in the final lines, "actions often have an effect exactly opposite from what is intended."
Madame Mathilde Loisel is a woman who feels misplaced in her life. She settled for a marriage with her husband Monsieur Loisel solely because she was not able to marry "higher." She resents the simple home they share and its sparse, plain furnishings, and while her husband dines heartily, she dreams of the riches and finery of the life she feels she should have had. So resentful is she of her present situation that she even spurns a friendship because the woman is wealthier than she, and the envy this creates for her causes her intense suffering.
When her husband presents her with an invitation to a ball, and then with the money to buy a new dress that she feels will be worthy of the image she wishes to present, she still feels she cannot go without the proper jewelry. Her husband, wanting nothing more than to make her happy, suggests she borrow a piece from her friend Madame Jeanne Forestier. Rifling through the jewelry, she fastens on a beautiful diamond necklace. With this stunning piece adorning her, Mathilde feels she can truly look the part she wishes to portray.
At the ball, Mathilde lives out her fantasy. She is admired, envied, complimented, and sought after. However, when arriving home, she realizes with horror that the necklace is missing. Following fruitless searches, she and her husband buy a replacement, and Madame Forestier is not told of the loss. This begins a ten-year endeavor to pay back the debts accrued. Mathilde, during this time, knows poverty, sacrifice, and back-breaking work, and the woman she becomes is a mere shadow of the woman she was before the ball.
When she encounters Madame Forestier after the debts are finally paid, her friend is shocked to see these alterations, and when Mathilde relates the story of the missing necklace, the replacement, and the years of toil and deprivation, Madame Forestier reveals the stunning truth - that the lost necklace was simply costume jewelry, worth a mere fraction of the replacement piece.
This is the situational irony of "The Necklace." The piece of jewelry that Madame Loisel used to escape the life she had for the duration of the ball was the vehicle for her descent into the life she now lives - "an effect exactly opposite from what (was) intended."