Screenwriting : Foreshadowing by Liran Dayan

One of my favorite examples of foreshadowing is in Shawshank Redemption when the warden says to Andy Dufresne, regarding the Bible, "salvation lies within". He has no idea;)

Foreshadowing is a device in which a writer/filmmaker hints at things to come; possible outcomes within a narrative. It's also used to create intrigue as well as avoid audience disappointment. Often characters will give some sort of prediction or perhaps a premonition, such as in Game of Thrones, "Winter is coming." Or, foreshadowing may appear in imagery or action, such as storm clouds forming on the horizon giving the hint that something bad is about to happen. :)

Another way to look at this: foreshadowing is the laying of hints or clues to the eventual climax of the story so that readers and audiences come away thinking it all makes sense when it's over. It creates an internal logic. So, too much foreshadowing allows us to predict the end and usually become bored with the story. Too little, and you end up with shock at the ending -- though that may make perfect sense for the story you're telling.