Oh god, I'm rambling again.
Icebergs (I love loanwords) are funny things. The reason I'm using them as a metaphor here is the way they swim. The largest part of an iceberg is, invisible to the common Titanic passenger, hidden under water. But it can still influence its surroundings, as the common Titanic passenger had to realize.
And now let's apply this to writing. Many concepts in storytelling should, if done well, be icebergs. How exactly that looks depends on the element, though.
One of the most common mistakes I've seen with people who want to present their game idea to the common public is way too much worldbuilding in the pitch. I already talked about plot in relation to the setting, so go read that post for more details. The bottom line is that the plot is what drives things forward, not the world it's set in.
Sure, you shouldn't completely ignore your setting. It exists for a reason, and not referencing it at all makes it interchangeable. But the other extreme, endlessly wallowing in the setting with hardly any plot, isn't much better. Make the setting matter, show things that need explaining, but don't cram every detail you have into it.
This is where my original inspiration for this post comes in. The book I read almost constantly threw its main characters' backstory at me, to the point where I started identifying them by what happened before the plot. As with the world, having actual backgrounds for your characters is a good thing. The things that happened in a character's past influence their decisions in the present. But that doesn't mean that these things should be elaborated every time they influence that character. Also, backstory is not an excuse for everything and characters should have at least some development over the course of the story.
Yes, even the plot can be iceberged to an extent. This refers mostly to overly detailed subplots that don't really add that much to the grand scheme of things. Alternatively, there's people who want to tell you every little thing that happens between important scene A and B, no matter how insignificant or matter-of-fact it is. This is like toilets in video games. Just because they're not in the game that doesn't mean that nobody poops. It's just not shown because it's irrelevant.
The Bottom Line
It all comes down to, well, paring down the things that are visible. I have the feeling that too many people feel that their audiences are morons and will not get things if they're not waved in front of their faces. Things can be left out. Things can be abstracted. We don't need to know that Bobby McJohnson's dislike of the color pink comes from the embarrassing hat he wore at his first day of school.
Also, this is one of these topics that's a highly uneducated opinion, so if I'm talking garbage, feel free to tell me. But include the non-garbage interpretation, too. Now, if you're looking for me, I'm in my tomato shelter.