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