When executed well, the technique of foreshadow and payoff, sometimes called call-forwards and call-backs, can pay dividends on multiple levels. It enriches your story and adds layers to characters. These can be in the form of an action, a prop or a line of dialogue.
In the film, LA Confidential, Ed (Guy Pearce) tells Jack (Kevin Spacey) how he made up a fictitious character named Rollo Tomassi so he could put a name to the person who murdered his father years ago, as no one was ever arrested for the killing. In this scene, we see that Ed is opening up to Jack about coming to terms with his father’s death, and we get some background as to why Ed joined the LAPD.
Later, when Jack is shot by the crooked cop, Dudley Smith, his dying words are “Rollo Tomassi.” This confuses Smith, forcing him to later question Ed about who he thinks Rollo Tomassi is. This tips his hand to Ed that Smith killed Jack, since Ed never told anyone else but Jack about this fictitious character.
This is a superb use of foreshadow and payoff, brilliantly executed by the writer where we get backstory, character revelation, and plot all folded into one. Study this film, as it is full of these types of gems.
In Back to the Future, we see Marty (Michael J Fox) full of self-doubt. He chats with his girlfriend, Jennifer, under an old clock tower, which was destroyed by lightning 30 years ago. A volunteer asks them to make a donation to save the iconic clock tower. They want to restore as it was before the lightning strike. Marty puts in a quarter and receives a flier. Later, Jennifer writes her phone number on it with the words “I love you,” to Marty, which he keeps safely.
When Mary is transported back to 1955, he needs a massive amount of energy to ignite the flux capacitor to fire up the DeLorean car and send him back to 1985. But the only thing capable of creating such force is plutonium or a lightning strike, which is unpredictable. But because he has the flier from 1985 mapping out the exact time when the lightning will strike, he can use that to return home. Incidentally the flux capacitor and the plutonium are also used as foreshadow and payoff to great effect.
Foreshadow and call backs are an important tool in your screenwriting arsenal. Next time you watch a film, note how these are used to enhance the story and enrich the characters.