So when you create your story, you have a few options. Some people create entirely new worlds, which is great for control, but man do you really have to pay attention. If you have magic, you have to create rules. If you have countries, they need a leadership model. There's so much to put together that it can be overwhelming. On the other hand, you can always just put things in an existing world. Saves a lot of time and hassle, but you have to make sure you know the world. That's why the general advice for first time writers is to "write what you know." If you're from a small mid-western town, make your character from a small mid-western town. If you've worked your life as a grocery clerk or a cashier, let your protagonist have a similar job. If you try to venture outside that, you're going to have to do some research.
We've all been there. You read a book or watch a television show and you think, "Jeez, that's not how cars work!" or "C'mon, no one from Montana talks like that." It's super prevalent in cop dramas, mostly because the genre has reinforced itself.
But at the same time, if you go full original, you better keep extensive notes, because you know your readers are going to point out that on page 127, the hero clearly used the magic feather without reciting an incantation, even though later, in chapter 14, it's stated plainly that the feather will not work without the incantation. Or perhaps your mysteriously side character mentions they used to be a thief, then your party gets stymied by a locked door. The reader's gonna be wondering why Mister Mysterious isn't picking that lock!
Point is, there's a lot of pros and cons to each. I've played with both, to be honest. My Nikrose story is completely original (or as original as High Fantasy can get,) so I had to invent magic systems, continents, kingdoms, animals, and so much else. It got really hard to keep track of it all when I just wanted to write! Contrariwise, I've written some humorous short stories about two goof balls in a small town. Easy to keep track of, no world to construct, I could focus entirely on the story... but it was lacking. No magic, literally or figuratively.
So I believe in The Paladin, I've found a middle ground. I haven't had to create a completely new world, I've just had to figure out how that world would react to the reality of demons and vampires. Now, whether I've made things easier on myself, I'm not entirely certain. I still have magic systems, per se, that I have to keep track of. I have rules for how creatures act and are killed. I have an entire organization of Paladins to figure out and keep consistent. But, at least they can sit down for a cup of coffee without me having to call it "jitter juice" or "energy elixir."
Be Excellent to Each Other!
Keep your eyes open for my debut novel, The Paladin.