Okay, Let Me Expand On That (Part 2)

"Novels are longer than you think they are." 8/24

Occasionally, in various areas of my work as a writer, publisher, and occasional teacher of creative writing (not currently, or even recently), I run into stories that the authors refer to as "novels" that are in the 60,000 word range. By and large they are also not remotely done. Once, literally once, one of these awkwardly sized creations covered the exact time period and emotional arc that it needed to, and was pretty well structured, but needed a lot more connective tissue and probably a couple of subplots. For the most part, they end way before the story does, sometimes with an epilogue or final chapter that would be a reasonable place to end the story if only we'd actually gotten there before we got there. It's very rare that these stories need to shed a third of their length and become novellas, dealing with a small part of their existing content, usually in more detail. Most of the time, they need to be longer.
I think a typical mass-market paperback is a pretty good approximation of how long a book is. They certainly seem to be a length that readers want to read and publishers think they can sell, so they have that going for them, but also people like books that length for a reason. It's a good length for a book. I grabbed a few off my shelf, and they're mostly right around 350 pages. My bookshelf also contains mass-market editions of Cryptonomicon and Very Far Away From Anywhere else, so obviously there's a range, but the middle of the bellcurve is right around 350 pages. I have never sat down with one and actually counted the words on a page. I have literally done that with the Circle of Magic books and Very Far Away From Anywhere Else, both of which have larger print and wider margins than most mass-markets for adults (VFAFAE is YA, but I suspect the layout choices had more to do with making it big enough to be visible on a shelf.) They each had about 200 words on each page. The Freelance Editor's Association defines a "manuscript page" as 250, which still seems a bit low for the actual page length of a normal book, but let's go with it. 250 words/page times 350 pages is 87,500 words. Not coincidentally, I also see figures in this range thrown around sometimes as about the optimal length to get a first novel accepted for publication. (Even authors known for writing long-ass books, like Stephen King and Neal Stephenson, did not start their professional careers writing things that were the size of dictionaries). That's a great deal longer than 60,000 words. More longer than it might feel like.
I think this might especially be an issue for people who have mostly written short fiction. Word limits at venues for short stories are a thing, and so is intensive minimalism training in writing programs. One of the big differences between a novel and a short story is that the law of conservation of detail is a lot less rigidly enforced. Not everything has to be doing at least 5 things to deserve its place on the page. You can have characters that get names and backstories that aren't going to be major players for the whole thing. You can describe something even if you aren't illustrating the world, the character's psychological landscape, the tone of the scene, and what you had for breakfast this morning. You're actually supposed to, or it's likely to end up feeling underdeveloped. Also, a lot of the details will end up serving multiple functions, but you may not recognize them immediately because novels are so much bigger and more time consuming that the planning to discovery ratio can't stay the same. You don't know what's going to matter ten chapters from now. You have a lot of space. Use it.
Also word limits create anxiety. I live with someone who writes short fiction, so I've seen it happen, the twitchiness when you realize you might not be able to keep it under 6000 words. It creates an instinct that however far past that you get, you're creating more work for yourself because you'll have to cut it down to be able to submit it anywhere. I suspect that this instinct persists even when you know intellectually that what you're writing is a novel, and doesn't need to be held to those same limitations. The longer it gets, the more nervous you get, because your feelings are thinking in terms of magazines.
Also, short stories tend to be smaller in time and scope, so often you complete the first third of a novel and get basically to the end of act 1 and feel like "Oh, I guess it's done now." Also, NaNo WriMo convincing people that a 50,000 word thing is a novel probably does not help with this.
So, if you're writing a first novel, I have two suggestions. First of all, describe everything and digress into backstory as much as you can. Second, aim for 100,000 words. Give yourself that as the space you're trying to fill, and the limit you're trying to stay under.