In the opening paragraph of the story, the author immediately tells us Mathilde looks herself as a "pretty and charming girl". However, she is unhappy for her state. She "let herself be married to a little clerk". She thinks she deserves to be rich. She also feels that she is entitled to have a more luxurious and elegant lifestyle. This is clearly shown when she refuses to attend the party without a stylish dress and fancy jewels.
When Mathilde finds out the lost of the necklace during the course of the evening, she replaces it with a new one. This is because she is too proud of herself. She rather not confronts her careless to Mme. Forestier which ends up takes away her middle class lifestyle. The Loisel spends 10 years of hard work to pay up everything, "everything, with the rates of usury and the accumulations of the compound interest." Over these 10 years, she surly learns the hardship of life, but does she learn the cause of her misfortunate?
The story does not say she does. Rather than thinking of how silly she was as a young woman, she thinks "of that gay evening of long ago, of the ball where she had been so beautiful and so feted." She is not angry of her silliness that ruined her life. She simply thinks "How life is strange and changeful! How little a thing will ruin her life?" She just blames it to the cruelty of fate rather than her own fault. All she understands is that life has played a cruel trick on her and she has suffered ten long years for nothing.
The advice Maupassant seems to give in "The Necklace" is "Don't get aspire for more then you have, it will ruin...