Well, it's not always in paragraph 3...but generally authors use foreshadowing as a psychological tool to prepare the reader for what is to come or to direct the reader to see or think something. Depending on the type and level of the writing, whether it's literary or popular fiction, for example, writer's can be direct, like making mention of a gun that'll end up being the murder weapon, or they can use dialogue to direct the reader to the character's mental state, which builds and unfolds the desired insight into the character.
