The setting is one of the most basic elements in a story. It sets the tone, paints a picture for the reader to imagine, and basically shapes the story itself. Without the setting the story could be set in anyplace anytime. You could have a story about space aliens corrupting the inhabitants of mars, but it's set in a ranch in the early nineteen hundreds. It just doesn't make any sense. If you don't have a setting, you don't have a realistic story.
When you have a setting, you set a mood, consciously or not.…