Take this position: Writing comes from a writer's imagination--not true
I'm guessing you are being asked to defend a position whether or not you agree with it.
Writing does not come from a writer's imagination. Writing comes from the writer's personal experiences. Take Orson Scott Card for instance. While the plot, locations, and characters in Ender's Game are obviously fiction, Ender, Valentine, and Peter are all based on parts of Card's deep Mormon beliefs. Much of the text in the Enders series are quotes taken from the Book of Mormon. That's not Card's imagination, that's his experience.
I was fortunate enough to have Gary Schmidt, a Newberry award winner, as a professor in college. He frequently spoke about his character creation process and how he would ground his character's emotions and responses based on past events that he himself lived through. If he had gone through a breakup, that heartache that he is intimately familiar with allows him to write it for any character of his choosing.
The heart of any piece of literature is the emotions that the author can convey to the reader. If the novel/story/etc. is simply a dialogue of events and moving from place to place, it reads like a travelogue or textbook. There isn't much "heart" in it. An author needs to be familiar with types of people, places, events, emotions, ways of thinking, etc. in order to really bring a plot and characters to life for the reader. That kind of knowledge can't be faked and make up. It must come from the author's own experiences.