How was, Mrs. Matilda Loisel 'a mistake of destiny'?

Answer – Mrs. Matilda Loisel was born in a poor family but she was vey charming and pretty. She appeared to be a lady of high family. Her parents did not have enough money, she was married to a clerk. She wanted to lead a life of Luxury and Comfort. So, the writer says that she was 'a mistake of destiny'.