If you are a writer of fiction, you have to have a good imagination. You have to be able to create imaginary characters, stories, settings. Fiction is a work of good imagination.
Children have the most wonderful imaginations. They let their imaginations run wild and free and create whole worlds in which to play. As adults, we have become accustomed to reining in our imaginations. We have to be an adult, act like an adult, and use our imaginations only in controlled circumstances, like writing fiction. We can’t live in fantasy worlds lest we hurt other people.
When a writer embarks on a work of fiction, it is a difficult transition to make. They are suddenly allowed to let their imagination, at least as it relates to the story they are writing, run wild and free like a child’s imagination. It has to be a bit more controlled in order to tell their story.