In my opinion, the inciting incident is the attendance at the ball itself. Because what follows creates the major conflict in the story, the loss of the expensive diamond necklace.
"Not until they are back in their humble house does Madame Loisel realize that she has lost the diamond necklace. Her husband spends several hours retracing their steps but finds nothing. They decide to replace the necklace without telling Madame Forestier, and they go heavily in debt."
The major conflict in the story is the hardship that the Loisels endure to replace the necklace. Their lives are controlled by the need to pay off the debt that they incurred to buy a replacement.
An inciting incident is normally reserved for dramas (plays):
The inciting incident is a plot element and arrives near the beginning of the drama. It can be long or short and connects the situation that the characters find themselves at the beginning or before the play begins to the end of the play. It begins the action and also sets up the main question (Motivating Question) that the audience wants the play to answer. The focus, therefore, is both on the character and audience suspense. (Bruch)
In "The Necklace," a short story, the inciting incident would be when the Loisels are invited to attend the ball. At this point, when Mr. Loisel tells his wife, Mathilde, that they've been invited to the ball, she panics and says she cannot go because she has nothing to wear (This is not true. She simply wants something expensive to wear in order to make it appear she has more money). Her husband has been saving money for a special purchase for himself, but agrees to let Mathilde purchase a nice dress for the ball. He then suggests that she go to their friend Mrs. Forrestier to borrow some expensive jewelry to wear. This scene begins the action of the play and sets the plot in motion.
Loises are invited to attend a ball.Mathilde wnted to buy a new expensive dress as to impress people that she got lot of money.
Madame Loisel feels that she was born for luxury. She is a beautiful woman and believes that she should be living an aristocratic life, draped in fine clothes, jewels and furs. She imagines herself to be living a life opposite of what her true destiny is, a life of meagerness.
It is because of Madame Loisel's deeply held belief that life has cheated her out of her due, that results in her reaction to the invitation to the fancy party. The party, Madame Loisel feels is where she should be, therefore, she must look the part. Madame Loisel is a Cinderella in reverse. She gets to go to the ball, and instead of losing a glass slipper, she loses her friend's necklace.
Her life is then turned into an existence of hardship and hard labor. She ends up in rags.
Monsieur Loisel is a hard-working man who loves his wife, but does not understand her. He wants to please her, and makes sacrifices to give her the luxury, if only temporarily, that she so craves. He is a simple man who is satisfied with his social standing in life. He has no aspirations to be among the aristocrats like his wife. He is content with his simple life.
Both these characters share some reponsibility for the hard work they endure to buy a new necklace. Individually, and together, they do not trust the rich, Madame Loisel, out of envy and jealousy, and Monsieur out of a sense of fear. He is afraid of the power of the rich