Every important event in your story has to be set up and foreshadowed. Otherwise your story can feel artificial and contrived.
Take any bad movie and you’ll find characters saving themselves through actions or devices that never previously appeared before. In “The Phantom Menace,” the two Jedi knights get trapped in a room that’s filled with poison gas to kill them. Things look bad until suddenly we see that the Jedi knights used The Force to save themselves from the poison gas and they’re okay.
To make this scene believable, we need to see an earlier scene where we see how The Force can help a Jedi knight avoid breathing toxic fumes. Without this earlier foreshadowing, the revelation that The Force can keep two Jedi knights from breathing poisonous gas just seems awkward and phony.
Now look at the original “Star Wars” movie where Luke sees Darth Vader kill Obiwan-Konobi, and Obiwan’s voice tells Luke to run. This sets up the later event when Obiwan tells Luke to trust the Force before firing his photon torpedoes into the Death Star.
Because the ability of the Force to let a dead guy give advice was foreshadowed, it made sense later when it was really necessary. Good movies set up events while bad movies just spring them out of nowhere for the convenience of the story.
In “Robin Hood” with Russell Crowe, Robin Hood meets Marion and to fool the servants, Marion has to invite Robin to her chamber. She does so, but warns Robin that she sleeps with a dagger and will cut off his manhood if he makes a move against her.
Later, this foreshadowing with the dagger pays off when French soldiers invade Nottingham and one soldier tries to rape Marion. When she pulls a dagger from a hidden sheath on her leg, we get a flash of recognition because we already know she has a dagger with her. Rather than rescuing her with a dagger that appears out of nowhere, we see that the dagger was already introduced earlier and its appearance makes logical sense.
Every good movie foreshadows important events. In “Thelma and Louise” we see Thelma packing and taking a gun along. When Louise uses this gun to shoot Thelma’s potential rapist, we see that the gun was set up earlier.
The lesson is clear. Always, always set up your important events ahead of time. Doing so makes your story feel more natural. Omitting this makes your story feel fake and contrived. Just compare “Clash of the Titans” with “How to Train Your Dragon.” The later film carefully sets up the events and items that will ultimately help him succeed while “Clash of the Titans” is just a special effects movie totally devoid of substance. As a result, this movie sucks while “How to Train Your Dragon” has drawing power, and that’s what you want from your story as well.