What a character knows can define what kind of story you are telling.
If you want to write suspense, the reader knows what the character doesn’t. You know that old line from Hitchcock where you show the audience the bomb under the table that the characters are unaware of. Or Michael Myers standing beside the hedge–watching, waiting. That’s all creating suspense–anticipation.
In mysteries, you will have characters know something that the reader and other characters don’t. The reveal generally solves the mystery.
In a lot of fantasy stories, you’ll have one character that knows practically nothing (Luke Skywalker) meet a character that knows everything (Obi-Wan Kenobi). The reader learns while the character learns. Characters like Luke Skywalker or Neo (THE MATRIX) all exist to allow exposition to be shared. Like that new guy on the job that HR takes around and introduces to everyone as they explain when and where they can take their breaks and how to use a time clock.
These are characters at the mercy of the knowledge of those around them. Morpheus could be lying. Obi-Wan could have had ulterior motives. Whenever you present whatever knowledge that your character has been holding back can either create suspense for the reader or become a shocking twist.
Imagine if Luke knew Darth Vader was his father the whole time, and was simply playing dumb to deliver his nemesis Old Ben to earn his father’s favor? When you reveal this makes a difference between whether or not you’ve created a twist or suspense.
The twist could be delivered when Obi-Wan yells at Luke to go–and Luke just stands on the landing platform, arms crossed and smirking as Vader informs Obi-Wan that his son has already joined the dark side. Shocking! This blond-hair, blue-eyed dweeb from Tatooine is evil!
Twists generally come at the end of an act. But it doesn’t have to be the last act.
There are some great horror movies whose twists are revealed pretty early on that change the reader’s anticipation. The recent BARBARIAN (2022 directed by Zach Cregger) is a great example, and an even better one at showing how once the twist is revealed, suspense can be sustained as another character enters the fray with the audience knowing what he doesn’t.
If you don’t like twists, but still wanted to create suspense, you could tell your readers when Obi-Wan says Vader killed Luke’s father, that Luke knew the story much differently. It was Obi-Wan who cut off his father’s limbs and left him for dead. Then the story would have the same impending ticking clock of a bomb beneath a desk as Luke manipulates the poor old Jedi into a fight he cannot win.
Try to be mindful of when a reader learns the information that you know as the author. In order to pull off the twist appropriately with Luke Skywalker, one would’ve had to seed that moment. Perhaps he ‘accidentally’ uses the dark side, and Obi-Wan scolds him while Luke plays like he didn’t know. Perhaps he lets something slip to another character that he would only know about the Death Star if he had already been on it.
Whether you want to create suspense or a shocking twist, be mindful that when you tell your characters or show your readers what’s in store for them makes all the difference.