When writing, and also when doing research for writing, it’s important to get the details right, but that doesn’t always mean what you might think. Economy of detail is usually better than excess, which raises the critical question about which details matter most.
The overriding principle to keep in mind is that of verisimilitude: making it seem real, without necessarily having to be wholly accurate or complete. Verisimilitude isn’t truth or correctness, but rather the appearance of those things. The usual way to achieve the latter is just to use the former — genuine facts — and that’s fine, but we’re still left with the matter of selectivity. Most genres of fiction won’t tolerate exhaustive detail very well; pace will falter, and readers will become bored. Instead, what you want is a judicious amount of detail that punches above its weight.
There are two pieces of advice I can give you here. The first one is to find what I call yellow postboxes. Our postboxes (public mailboxes for the sending of letters and such) here in Scotland are mostly red, in the livery of Royal Mail. In the US, most postboxes are the dark blue of USPS. What’s normal to you is likely different elsewhere, and it’s knowing these small details that conveys authenticity in a concise, economic way, especially if it also teaches the reader a piece of trivia which they can then regurgitate in future.
You’ll find red postboxes in Italy too (but not in Vatican City), whereas in Spain they’re the bright yellow of Correos. I was surprised and delighted by these yellow postboxes the first time I saw them as a child, and they’ve become emblematic of a mundane, minor detail that effortlessly says this is authentic. Those details are the best way to confer verisimilitude.
Instead of trying to showily prove that you know what you’re talking about, by force-feeding the reader a mini-thesis about whatever your scene focuses on, instead distil it all into one or two seemingly-trivial details that would only be obvious and recognisable to someone who really does know about that thing. For whatever you’re writing about, find the yellow postbox.
Pin your detail into the scene in a way that feels almost assumed, and offhand; the effect will be an equally-effortless authoritativeness, delivered so casually as to be undeniable. You don’t ever want the reader to consciously think the author really did their research. Instead, you’re shooting for huh, I didn’t know that; that’s interesting, then they go and tell their partner as soon as conversation reasonably allows, in order to seem educated and worldly. You know exactly the feeling and the scenario I’m talking about.
Which brings me to my second piece of advice, closely related to the first: be wary of drawing attention to yourself. Outside of some niche techniques or genres, you generally want the reader’s entire focus to be on the fictional world of your story, and not at all on you, the author. If you accidentally do something which causes that focus to shift back out of the story, it’ll be jarring for the reader, it will come across as amateurish, and it’ll affect enjoyment of the tale. If you’re doing it deliberately, fine; more power to you. But don’t let it happen unintentionally. One of the ways you can cause such a shift is if you project your own knowledge onto a character who wouldn’t conceivably share that knowledge. This happens mostly when authors want to show off how much they know about something, or more likely how much they’ve just recently learned about it while doing their research. It’s easy to forget that verisimilitude isn’t just about details, but also whether or not a given person would actually know those details.
If a postman had just finished emptying one of those yellow postboxes and went into a coffee shop for refreshments, then was unfortunately shot by someone who was trying to rob the place, would the poor victim really be aware that due to the rate of blood loss, he only has about forty seconds of consciousness left? Would he know why his heart rate was increasing instead of decreasing? Would he know that he was going to die of suffocation rather than directly from hypovolemia? It’s possible, of course, but it feels doubtful in general. Depending on your narrator’s voice, you could be unwittingly projecting that knowledge into the wrong-place-wrong-time postal worker’s head. Some of your readers are going to frown, and feel that something isn’t right. Many of them won’t be able to articulate why, but you’ve created a sort of literary speed-bump for them.
(Here’s a free yellow postbox for you: in the UK, speed-bumps are or at least were known in some regions as sleeping policemen, for precisely the reason that the mental image suggests, which I think we can agree is just linguistically delightful.)
Maybe the Spanish postman would see his own blood soaking into his parcel bag, staining the logo (it’s a trumpet with a crown above it, in even brighter yellow!) a gruesome shade. But he probably wouldn’t be theorising as to how exactly a surgeon might save him from a medical perspective, if only the EMTs are quick enough to arrive. I can understand why the author would have looked that stuff up, but it’s really not destined to fit into the shooting scene itself. For a later scene at the hospital, yes, that would work — but for now, it’s just the author showing off their ability to read wikipedia. Be wary.
Research is a distillation. You’ll spend two hours reading, to get four paragraphs of notes, which provide eight words of story — but those eight words will take the reader into the world you’ve created, and create the impression that your character really is there, or really knows about this topic. Just make sure it’s either unremarkable that they would know those things, or that their knowledge has been explicitly accounted for.
Did you know that, in the 1970s, postal workers here could decline to deliver the leaflets of political parties they didn’t personally support? Did you know that the illuminated “for hire” or “taxi” sign on the roof of a licensed taxi here is colloquially referred to by drivers as the begging light? Life is stuffed full of fascinating bits and pieces like those. That’s where verisimilitude lies.
Keep a large stock of those treasures, always be on the lookout for new ones, and above all, use them sparingly.