* Circumstances: She grew up in a literary household, surrounded by intellectual discussions and famous writers. Her parents, Mary Wollstonecraft and William Godwin, were influential figures in the Enlightenment, and her step-father, Percy Shelley, was a renowned poet.
* Need for expression: The loss of her mother at a young age and the tumultuous, passionate, and ultimately tragic romance with Percy Shelley all contributed to her deep emotional needs. Writing became a way for her to express herself, her thoughts, and her feelings.
* A creative challenge: The famous story of the creation of "Frankenstein" as a result of a challenge amongst a group of writers during a stormy summer is a testament to her inherent creativity and desire to explore new ideas.
* Financial necessity: While she was born into a privileged world, her life was marked by poverty and financial instability after her marriage to Percy. Writing, especially the success of "Frankenstein," became a source of income and a way to secure her own independence.
In short, Mary Shelley's journey into authorship wasn't a planned career path, but a response to her circumstances, her emotions, and her need to express herself creatively.