In what ways is Mathilde Loisel responsible for her own downfall?

Mathile is responsible for her own downfall because of her pride. Her pride won't allow her to attend the party she dreams of without the perfect dress and jewelry. Her pride doesn't allow her to believe that a monied woman would own anything except the "genuine" article. She assumes the jeweled necklace she borrowed was real, simply because she believed its owner would never wear paste. Her pride also keeps her from admitting her mistake and confessing the loss to her friend, an act that would leave her (and Mr. Loisel) destitute.