The object of most of your writing is to tell a story, whether it's fictional or not. The story will have a beginning, a middle, and an end, and in telling the story, you are moving the reader along, maintaining interest and attention from page to page. To facilitate this, the writer has at her disposal an array of devices--species of writing like narrative, exposition, dialogue, background. Each stage of the process has its own particular challenges.
Ian Jackman, The Writer's Mentor, 2004