Answer:
In my understanding, Mathilde's obsession with material possessions and her desire to belong to a higher social class were the primary factors that led her to spend her life repaying a debt that was never real. Her character flaw was her lack of contentment and her constant yearning for more, which blinded her to the fact that the necklace was fake. Fate and irony might have played a role in the story, but ultimately, it was Mathilde's actions that led to her downfall.
Perhaps, Mathilde's situation was preventable if she had been content with what she had and appreciated her simple life. Instead, she pursued a life of luxury and extravagance that ultimately led her to misery and hardship. The story serves as a warning against the dangers of materialism and the importance of being grateful for what one has.