What is it, you ask, and why might I want to avoid it?
After a bit of judicious prodding, the internet spat back a few relevant definitions for oversell such as: “to be too eager or insistent in attempting to sell something” and “to make excessive claims”. For the most part, the word oversell is used in sales to describe ridiculous nonsense being claimed to try and sell a thing or the act of being super pushy and used-car-salesman-y. Or it’s used to warn interviewees away from making themselves sound too good to be true so that the interviewer’s bullshit meter starts to flash, or the new hire fails miserably because they promised all sorts of stuff they couldn’t do. I have no idea why, but for some reason, I yoinked the concept of oversell and applied it to writing fiction. (And if you find oversell by another name elsewhere with respect to writing, I’d love a link. :))
Oversell, how I use the term, is when you’re writing along (or editing along) and come across a phrase, sentence, or paragraph that pushes the idea you’re trying to convey to the point where it’s noticeable that you’re pushing. To use a movie analogy, oversell is the moment takes the movie past decently executed with purposeful cinematography and into the realm of obnoxious 3D fish flying from the screen to make you duck. Or that moment in Gravity where you go, “Oh, it’s a space womb,” or in the latter Matrix movies where you go, “Wow, crucifixion imagery and Messiah parallels. Thanks for that. Never would have caught that. Really.”
Oversell in fiction is similar. It’s explaining the joke, or stating outright the theme of your story as if your audience wouldn’t pick up on it otherwise. It’s that ‘extra’ little bit that makes the audience go ‘Alright already! We get it! Move on!’
Why you might want to avoid oversell:
There is no reason why you need to hand your audience/readers the answer. A sub-function of show-not-tell is the 2+2 principle.
The 2+2 principle is where you offer your readers all the pieces and let them put it together. The reader is the one who ultimately figures out that 2+2=4, and you never actually tell them that 4 is what you were aiming for.
This serves two purposes.
One, you’re not just handing them the conclusions you want them to reach. Not only are you exercising a narrative ‘tell’ by providing the conclusion, which leads to a flat narrative, your conclusion might not be the conclusions your reader would reach on their own, so then they feel like they’re being preached to. If you’ve ever read a review that called a book (or other piece of media) ‘preachy’, they’re talking, in part, about oversell.
The second purpose behind 2+2 is that, by handing them pieces and requiring your reader to reach a conclusion, your reader now must invest some small amount of effort and brainpower into their reading experience. As a result, you’ve set your reader up to get that tiny rush of satisfaction in the ‘click’ moment. Terry Pratchett’s books are absolutely boss at utilizing the 2+2 principle. Any book with a really brilliant ‘oh shit’ or ‘oh my god’ or reveal moment has succeeded in giving you all the pieces and then providing you with the opportunity to put them all together.
Oversell overrides 2+2. While you still may be showing the answer (in a show-not-tell sense), you’re also showing the answer, which is the opposite of what you want.
In a more practical sense, oversell is also just pointless extra words. You’ve already made your point, you don’t need to make it again. Half of presenting an idea or an argument or a piece of creative work is knowing when to cut and run.
Last – er – maybe it’s just me, but oversell (in the most egregious examples) is super annoying. I have a gut ‘don’t tell me what to do’ reaction. There is a sense, like I said above, of ‘I get it already! Just keep going! We don’t need to dwell!’ combined with a ‘well, I was on board before, but now you ruined it.’
I don’t get annoyed by small bits of oversell, though. Partially, that’s because I’m super guilty of oversell in my own work, and I mostly catch it during the editing phase. The part of it is that I see it all the time in published works. It’s where an author just goes notion too far before moving on. It’s common and, to be honest, most of the time it’s not glaringly obvious. When I’m being a Reader (rather than an Editor), oversell is one of those things that becomes a nuance. It disappears into the work, for the most part, same as weird names or other small decisions that don’t impact the story so much as the telling of it. A good story can make up for a multitude of tiny imperfections.
Plus! Sometimes oversell can be a trick in and of itself, like when explaining the joke is the joke (Link is Dr. Horrible. Slightly nsfw, heh.), but most of the time you’re undermining your own piece by not letting it stand on its own merits.
Last thing: don’t let a worry that you’re overselling stop you from writing. Oversell is an editing-level concern. Even if you’re a one-pass gut-level writer who never changes a single word you write (except typos), oversell is very easy to fix. 99% of the time you can simply cut out the line or the paragraph entirely and the work is not just unchanged, it’s stronger. Sometimes, too, you can’t tell where you’re trying too hard until you read the whole thing through after you’re done.
Above all, though, don’t be afraid to let your work stand on its own. Trust your words will lead the reader to the conclusion you want, and you’ll avoid a lot of oversell.