Obsessive overbuilding
The flip side of forgetting about the implications of all the things one puts into one's worldbuilding is becoming obsessed with getting every detail just so. It is a great way not to produce a lot of finished writing.
Overbuilding an imaginary world is a problem that is closely related to over-researching. They have similar pitfalls both before and during the writing process: there's the tendency to get so caught up in researching/inventing details that one keeps putting off the actual writing (in extreme cases, this results in the person abandoning writing altogether, and taking up worldbuilding/researching as a hobby); and then there's the tendency to try to pack all of the research/invention into the story (also known as "but I can't waste all that work!" and "I suffered for my art (doing all this research); now, Dear Reader, it's your turn…").
It is, of course, a truism that the writer knows more about the world, its history, and the background and backstory of the characters, than ever gets into the story. The thing that seldom comes up is the fact that when the writer knows it and how much the writer knows are things that vary from writer to writer and book to book. The most extreme examples at either end of the scale are those writers who sit down in front of a blank screen and make it all up as they go along, and those other writers like J.R.R. Tolkein, who spent somewhere between forty and sixty years developing the world of The Lord of the Rings.
In between are the rest of us, varying from one end of the scale to the other in terms of how much worldbuilding we need to do before, during, and after writing a story. Yes, after - it's not unusual for a book to require more worldbuilding to resolve plot-and-consistency problems discovered during the rewrite, and it is exceedingly common to need more worldbuilding when one is writing more than one book using the same setting. I made up steam dragons, daybats, spectral bears, and swarming weasels for Thirteenth Child, but I didn't nail down the entirety of the magical ecology of the Western plains and the Rocky Mountains. So there are a lot of new critters in Across the Great Barrier that I didn't know existed until I needed to mention them, even though I'd already written an entire novel in that world. I still don't really know anything about the magical ecology of South Columbia, Aphrika, Avrupa, etc. I know it's there, and that it's different from the ecology of the part of North Columbia I'm dealing with in the books, but I don't need to know the details unless and until they come up in the story.
On the other hand, I know way more about cinderdwellers and steam dragons and assorted other things than has made it into either of the books I've written so far (and it doesn't look like getting into the new one, either). Some if it is written down; some isn't. This pattern holds for everything, from the politics and history of my world(s), to cultures and customs, to things about the family: some of it is written out, some of it is still just in my head. I also do not require myself to stick strictly to every worldbuilding decision I've made - as my friend Lois says, "A writer should always reserve the right to have a better idea." There are always a few things that are non-negotiable, but most things, I'm not stuck with until I've used them in the story, and sometimes, not even then.
I work this way because it suits the way my imagination handles things. I require a basic framework for my background, but it can't be too detailed. Without the basic framework, I go into choice paralysis - I could have any kind of setting, background, history, without limit, and my brain seizes up at the prospect. If the framework is too detailed, though - if I've made the mistake of trying to work out an entire imaginary encyclopedia of background - then I start feeling constrained and tied down. Too much detail, for me, makes it feel as if I were writing real-life mimetic fiction, without enough freedom to make up the stuff I want.
That closed-in feeling - the sense that you have to check every other noun against your encyclopedia to make sure you're being consistent with all that background that isn't even in the story - is the surest indication I know that the writer has produced more background in more detail than they really need in order to get on with the story. And that itchy point will be at a different level of background information for every writer. Some folks need a three-inch ring binder full of notes on everything from weather to favorite foods to different cultures; others get twitchy if they have more than a few key facts tied down before they start writing.
The trouble is that the itch doesn't show up while you're doing the advance worldbuilding; it only shows up once you start to write, and by then it's almost too late. There are a few other signs of overbuilding a world; one of them is creating Tolkein-esque mountains of material that you find boring to read through. The whole point of writing down aspects of your worldbuilding, for a writer, is so you can write the book without forgetting key points or ending up with major inconsistencies. "Enough worldbuilding" equals "however much YOU need to have in order for the book to be coherent, believable, and consistent." Whether your background notes are in the form of a glossary, an encyclopedia, a tiddlywiki, a single page of bullet points, or whatever - if they aren't useful and accessible to you, while you are writing, there's not much point in having them.
Doing a lot of worldbuilding in advance is not a requirement for writing a fantasy/SF novel. It's one possible way of getting to the desired end, which is to have a believable portrayal of a world in one's novel. Whichever way you work - doing it in advance, or making it up as you go - if the result isn't coherent and consistent and believable without interrupting the story, you have a problem. Ultimately, the solution is yours to figure out, because your solution is going to have to work for your particular brain and writing process. It is, however, a good bet that if you have such a problem, the solution is unlikely to be "do more of whatever you were doing that got you into the problem."
If what you are doing isn't working, try something else.
