Some stories are happy, sad, angry, etc. Every story has a distinct mood, and words show that. In a happy story, sad words aren't going to be used. The author should use words that match the target audience and mood they are shooting for. Moods can make the reader want to read your book, or completely turn them away from it. Certain readers love to read dark books, and others like to read books with a more positive, upbeat feel. When writing, your word choice will directly affect the mood of the story. Certain genres follow different moods. A suspense, action, or espionage novel will normally have a suspenseful feel. When writing your next story, watch your word choice and try to make them fit for your novel.