It doesn't really matter who said it, it's so obviously true: Before you can write anything, you have to notice something.
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.