Here's what we know:
* Olivia's illness played a significant role. Olivia was diagnosed with a rare blood disorder that required numerous surgeries and hospital stays. Dahl, desperate to entertain his daughter during these difficult times, began telling her fantastical stories. This experience sparked his interest in writing for children.
* He was already writing. Dahl was already a successful author, known for his adult short stories and novels. However, he found a new creative outlet in these stories for his daughter, and he realized that children's literature could be a powerful medium.
* He didn't intend to be a children's author. Dahl initially intended to write these stories only for Olivia. However, when he shared them with other children, he found that they were enthusiastically received. This convinced him to publish them for a wider audience.
So, while Olivia's illness was a catalyst, it wasn't the sole reason for Dahl's foray into children's books. He was already a writer, and the experience of connecting with his daughter through stories opened up a new path for him.