When does a chess game become boring? The moment you know who will win. In fact, oftentimes the players will simply restart the game right then and there. What's changed? There's no longer any uncertainty. Uncertainty is a driving element of story engagement. And it's at the heart of suspense. But uncertainty alone isn't enough to create suspense. So, what is suspense? Or maybe a more helpful question: How do we create suspense?
Suspense is created by the anticipation of imminent, uncertain information of perceived consequence.
There's a bit to unpack in that definition. First, let's start with "anticipation". Anticipation arises from the expectation of currently uncertain or unknown information.
There are two main elements of anticipation: imperfect information and the expectation of that information. There are various methods for letting the audience know that they have imperfect information but they most all boil down to the posing of an implicit or explicit dramatic question. For instance: Who's this hooded figure? Will she make this jump? What's in his pocket? What's on that paper? Where will the meeting occur? Who's side is he on? When will she find that key?
So we've posed a dramatic question. The next step to create anticipation is to set an expectation that the obscured information will be revealed. The best method for doing that is to imply that the information has dramatic significance by giving it narrative weight. What does that mean? In short, imply that the information is important by focusing on it. There are a number of techniques to imply that information is important and a good many of them can be found under the topic of "foreshadowing." To give a story element narrative weight, give it more attention in time, space, intensity, or context. The more important the story element appears to be, the more the audience will come to expect its identity or effect to be revealed.
Consider the opening of Hitchcock's "Notorious". Alicia is hosting a party and we see the silhouette of the back of a man in a chair. He says nothing, but he consistently stays in the frame. Alicia talks to him but there's no response. She serves him a drink, but no response. We wonder who this mystery man is and our interest grows as Alicia continues to engage with him but receives no response. She kicks everyone out of the house except for him. Finally in the next scene, the camera reveals his face. All the buildup, focus, and character reaction lets us know that his identity is important. It increases the narrative weight. We anticipate the reveal. Notice, however, that while the reveal of this man's identity is eventually consequential, it is not apparent that it will be immediately consequential and thus does not fulfill the prerequisite for suspense.
Oftentimes importance is inherent. We already know that a fraying rope with our protagonist dangling for her life is important. The situation provides a natural expectation that the answer to the question, "Will the rope snap?" will be revealed to us. These scenarios come with an expectation that the important question will be answered. To completely abandon answering these important questions is near malpractice from a storytelling perspective. The audience will want the answer eventually.
So to create anticipation, create an expectation that imperfect information will be revealed. Note, however, that anticipation itself is not the same as suspense. We can anticipate that an identity will be revealed, but if we don't wholeheartedly believe the information to be of consequence then we will not feel suspense.
Want to increase suspense? Increase the importance of the uncertain information.
Consequence and Concern
Here's the cold truth about story information: we only care about it if it's consequential. That is to say, we only care about information that will have an effect on other things. This is often why the worldbuilding culture and backstory you've been working on for six months is skimmed or skipped by the reader in an effort to "get to the good stuff." If you were to incorporate that information in such a way that the information had a consequential effect on the outcome of the story, then the information would garner attention.
This is especially true of suspense. We can create an expectation that information will be revealed but if the audience doesn't have the strong sense that this information has clear implications and will be immediately consequential then the audience won't feel suspense. The possible implications of the reveal must be apparent beforehand (even if those implications were incorrect).
This is where stakes come in. Stakes are all about consequence--they're the consequence of an outcome on a character. In other words, stakes are what a character "wins" or "loses" when the outcome of a question is revealed. For instance, let's say that our dramatic question is, "Will the frayed rope snap?" If the outcome to this moment is a snapped rope, the protagonist plunges to her doom and "loses" her physical safety. If the outcome of this moment is that the rope maintains its integrity with enough time for the hero to pull herself to safety, then the protagonist "wins" her physical safety. Implied in the frayed rope is a consequential outcome. The physical safety of the protagonist is at stake. The answer to a dramatic question should affect other, larger questions.
Information of consequence has a subtle implication. Namely, consequential information affects a character about which we are concerned (whether positively or negatively). In short, that means we have to care what happens to the character in order for the outcome of the uncertain information to matter. Be sure you've created a connection (whether positive or negative) between the audience and the character using techniques of empathy. We will either actively root for the character's success or actively root for their failure. But either way, we must have a preference in order to truly care about uncovering uncertain information.
Want to increase suspense? Raise the stakes. Make the consequences matter. Make us care what happens to the character. Make the reveal of the dramatic question immediately affect a character with which we're concerned.
In the context of suspense, urgency consists of two parts. First, why does it matter that the dramatic question is answered sooner rather than later? Secondly, what's forcing the reveal?
Generally, a dramatic question needs to be answered sooner rather than later if it will affect the outcome of a larger question. And in this way, the affected characters should care that the information be revealed sooner rather than later because they want to use the information to answer a larger question. After all, if it doesn't matter to the characters when the information is revealed then why should it matter to the audience?
After we've established why the question needs to be resolved sooner rather than later, we arrive at the matter of what's forcing the outcome. To create increased suspense, there should be something forcing an unveiling of an answer to the dramatic question. In other words, there should be a deadline to the question--whether implicit or explicit.
There are three primary methods for imposing a deadline on a dramatic question.
Often this is an explicit deadline and usually consists of ticking clocks (such as ticking bombs, oxygen levels, carbon dioxide levels, timed approach of conflict, etc.). It's the explicit measurement of some amount or value that is headed toward a "trigger" of the outcome (with "0" often being the trigger).
A time constraint can also be implicit, however. Carson Reeves gives a great example in Titanic where Jack and Rose are having a hushed conversation in an exercise room on the first class deck where Jack isn't allowed. There's an implicit time constraint to their conversation for fear that they may be caught.
This implicit deadline is brought on by a lack of plausible alternatives to the outcome. In this way, a reveal of the outcome is all that's left to do. Sometimes the hero can be the one forcing the outcome because it's in their best interest to get the information to be used in a larger question. Other times, the hero wants to avoid the question (and usually the conflict) at all costs.
This is an implicit deadline usually brought on by the unavoidable approach of conflict. It's the natural coming together and thus clash between the protagonistic and antagonistic forces. An example includes a knife headed toward the hero. The classic example is of the detective rifling through an apartment while the killer is headed up the stairs without the detective's knowledge.
This deadline can also be thought of as an implicit time constraint.
Often deadlines are implicit in conflict. A quick example is someone lunging at you with a knife. This would be an example of convergence. You've got until the knife lands to do something.
Want to increase stakes? Make the outcome urgent.
Suspense is created by setting an expectation that consequential information (affecting a character about which the audience is concerned) will be revealed sooner rather than later. If you can establish each of these elements, you can create a feeling of suspense in your audience up until the moment that the dramatic question is answered.