I've been making suggestions about how to make any piece of writing more literary. In this case, I will talk about story unity. Have you ever read a piece wherein events, characters, and even climaxes seem sort of tacked on, to come out of nowhere? A good story is well-integrated, all events planned with foreshadowing and build-up. As Anton Chekhov tells us, "If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter, it absolutely must go off. If it's not going to be fired, it shouldn't be hanging there." In other words, if you're going to include some prominently displayed item, character, or symbol, it should be used somewhere in your story. It should be there for a reason, or you're wasting words and the reader's time. Conversely, if you're going to have a major event like a rifle going off at the end, you should hint at the possibility somewhere earlier.
There are several pitfalls to avoid, mainly with characters or events in the story that feel tacked on and poorly integrated. The first two are often associated with video games or television. The Big Lipped Alligator Moment, or pointless and unrelated and often ridiculous side event or character, seems to exist to fill space or distract. The name traces to a scene from "All Dogs Go to Heaven," wherein an alligator shows up for no reason in a scene unrelated to the plot. Giant Space Fleas from Nowhere are simply major antagonists (major bosses in video game terms) that don't tie into the story. There is no foreshadowing and no deeper meaning. A big baddie shows up, makes things harder for one scene, then is never seen or remembered again. Why are they there? Often, not even the author can explain them. If you can't justify major or minor events and characters in terms of your overarching plot, meaning, or character development, cut those scenes.
It is particularly important to build toward the climax of your story and to make meaning of it. When an author does neither, he likely has either a Deus ex Machina or Diabolus ex Machina, which are more literary terms. Deus ex Machina--God out of the machine--is when a literal or figurative hand of God shows up and fixes what's wrong. Some crazy powerful new ability or character shows up and saves the day. In The Stand miniseries, a literal big hand shows up and makes things better. Meanwhile, Diabolus ex Machina, or devil from the machine, is where an overly powerful bad guy who has not been foreshadowed, hinted at, etc. appears and makes things much worse for the heroes. The solution here is not necessarily to cut the character or event but to integrate it. Hint at it in a way the reader won't necessarily catch. If possible, make either good or bad relate to the main characters and/or come from the characters. Make it all seem possible within the world of the story. Basically, set up for it and then make sure it enhances meaning, character, and plot in a way that makes sense.
Literary greats usually build up toward minor and major events and characters then use them to build on their deeper meaning, plot, and/or characters. Yes, anything is possible in writing. However, if your reader finds scenes and characters far-fetched, unrelated, ridiculous, or distracting, you've lost them. They are thrown out of the world of the story and won't likely come back in a hurry. Everything you do in your story should be carefully planned, integrated, and meaningful.