I recently read a novel that was chocked full of details the author thought was cool, and he used them to spice up an otherwise dull storyline. All writers have ideas for scenes and details that on their own seem interesting, unique, real, or cool, but if those ideas don’t connect to and advance the basic problem of the story, they will take away from or muddy the waters of the emotional investment the reader is experiencing. A writer wants to heighten that emotional investment, not siphon it off. And let’s face it, if a storyline needs those cute little details to be interesting, then perhaps it’s the plot you should be working on.
To heighten the reader’s investment, every scene and every detail ideally should change or affect the central driving question that forms the backbone of the story. The two reasons that I’ve noticed that writers (and I do it myself) drift away from the core problem is:
1. They have a shortage of story, meaning, they don’t have enough conflict surrounding the central plot. They end up creating situations and including meaningless details, scenes, and dialog as filler to round out a story. Readers, generally speaking, are not stupid. They can smell filler a mile off and it pulls them out of the story as they struggle to understand how this affects the central problem.
2. They include something “real” and/or “cool” even though it doesn’t compellingly move the plot forward. This is not so bad when it’s simply details of who’s wearing what, or describing a room, but I’ve seen writers include several scenes and even chapters that were merely filler in an attempt to entertain the reader.
A story is about x, where "x" equals compelling characters and a central problem/question that propels us through the entire narrative. Anything else you include stands a good chance of diminishing the reader’s emotional investment.
Ideally, all elements should advance the central theme/problem. But all good scenes serve multiple purposes, and there can be room for informational, interesting, "real," or just "cool" elements that don't develop the main problem, as long as they are weaved into something that does -which should make up the main thrust of the scene.