Now, if you've planned out your novel well in advance, you'll wonder what I'm talking about. Surely opening a story and closing it up are the hardest bits to do, right? Well, technically yes. But here's a little fieldwork for you: go grab any fiction novel close at hand. In one hand pinch the pages that you would class as being the 'beginning' of that story, and in the other pinch what you would class as the 'ending'. Now, unless you've picked up a novel that is especially avant-garde, you're probably only pinching thin slithers of pages at each end, leaving the vast bulk of the novel in the middle untouched. This is the main headache most authors face when it comes to the 'middle' of the novel: the fact that it's so darn BIG.
And what does the middle of this novel do for the story? By and large it will see your protagonist proceed through a 'quest' of sorts, overcoming trials and tribulations to that final confrontation, the climax and resolution. To some authors, especially in some genres, this is easy: said quest is explicit and the trials can be laid out pretty clearly like a gauntlet. Crime and mystery novels can pace out the incidents and clues, and fantasy novels may involve a quest which is paced out by the progress of traipsing across a mythical land or collecting items, a la Lord of the Rings or Horcruxes in the final Harry Potter book.
But what if your novel takes place in a singular location? What if your protagonist doesn't face obvious obstacles on their way to confront their main foil? If you approach your project with a view of writing a full novel rather than a novella, the prospect of writing tens of thousands of words to take the protagonist across that bridge from the start of that journey to the end is a daunting task. Because to you, as the author who has planned this all out, the resolution may seem direct and obvious. After all, the protagonist has a problem that he or she needs to solve. Why doesn't he just go straight to the root of the problem and solve it? Character logic dictates this, and yet the author in you cowers at doing so, knowing your meticulously prepared story will resolve itself as quickly as it started.
The low skilled authors resort to padding. Bulking out the middle of the novel with useless exposition, lore, scene setting, all occupied by a protagonist whom the author seems to have made frustratingly thick or detail-obsessed so that they pussyfoot their way around that main conflict until the author deems that they have padded the word count out enough.
But it needn't be that way. Not if we follow the golden rule of questions. I've mentioned this before, but the major driving force that keeps your reader turning those pages are to find the answers to tantalizing questions that you've laid out. What did happen on the midsummer's night of 1983? Why is Timothy refusing to talk about the key-shaped tattoo on his neck? Who kicked Hayato off the rooftop of the festival Shrine? There should always be at least one question running through the spine of your novel that not only drives your story forward but also your audience.
And yes, it's okay to set up more questions as you go. But you shouldn't try to juggle too many questions without providing answers: it can muddle the clarity of the narrative as well as switch off your reader who may feel they're in the hands of an author who is trying too hard to keep them in the dark rather than develop the story. I'm looking at you, J.J. Abrams.
So what you do is, along with the characters and plot, these questions should also develop. So when you answer them mid-quest, answer them with "Yes, but..." Or "No, and..." In other words, the answer itself invites another question.
For example, there are many murder mystery novels and TV shows out there where we learn the identity of the serial killer well before the final resolution. From there spawns questions such as 'Why is he/she doing it?' and 'how will the protagonist deal with this?' The first season and novel in the Dexter series by Jeff Lindsay is a prime example of this.
These questions can inform the way your protagonists' quest shapes itself by introducing those "Yes but" or "No and" complications on the way and are a useful tool for integrating obstacles and plot twists for the protagonist to navigate, so it doesn't feel as though the middle of the novel is padded but the protagonist is grinding their way through real difficulties that keep threatening to throw them off course. Let's say our protagonist comes to a bolted door, behind which lies the answer to one of those tantalizing questions that will take them one step closer to their goal. But to open the door? Only Timothy, the man with a key tattoo on his neck, knows how! But for some reason he is deathly afraid of this door. Why is that? And how can the protagonist help Timothy confront his fear and open the door? And so on.
That vast middle passage of a novel can be deeply intimidating, but if approached with an intricate setup of questions and answers, it can not only be easily managed without resorting to padding but also provide the most scope for an author to really stretch their wings and take that narrative to new and interesting lengths, far more so than a mere beginning or ending allows.