John Irving, the author of The Cider House Rules, reportedly said:
It doesn't really matter who said it, it's so obviously true: Before you can write anything, you have to notice something.
And it's advised to write down what you have noticed.
Horne, Theroux, Boyt and Chaudhuri posted on The Guardian ‘Messy attics of the mind’: what’s inside a writer’s notebook?" (6 April 2018). In the post, they related the following about Henry James:
Jotting things down in a notebook is one way writers shape and discipline the unpredictable flow of ideas. For Henry James, in 1881, just after publishing The Portrait of a Lady, it was already a matter of regret that he had “lost too much by losing, or rather by not having acquired, the note-taking habit”. But he would make up for it over the next 30 years by filling innumerable pages with his records of story ideas, anecdotes from dinner parties and newspapers, things noticed on his travels. He developed personal rituals around the process of expressing his thoughts, through the pressure of pen on paper.
Thus, keep a cahier handy to jot down fiction that you may (creatively) turn into non-fiction.