Why does the woman suffer constantly in "The Necklace"?

Madame Loisel suffers endlessly for all of the luxuries she believed she deserved but didn't have.

She suffered endlessly, feeling she was entitled to all the delicacies and luxuries of life. She suffered because of the poorness of her house as she looked at the dirty walls, the worn-out chairs and the ugly curtains. All these things that another woman of her class would not even have noticed, tormented her and made her resentful.