Research is fractal. The more you do of it, the more you know you have to do.
Research is essential. Unless you’re drawing all of your fiction from your own lived experience, you’re going to have to look things up, try things out, go to places in person to see. And even if you are drawing all of your fiction from your own lived experience, you’ll still need to double-check and make certain that your memories and recorded reality match up. (The near past is possibly the trickiest of all eras to write in. Just keeping track of things like when cell phones went from being expensive, bulky, and rare to being cheap, small, and ubiquitous can be a writer’s nightmare.)
Research is impossible. No matter how thoroughly you research your material, there’s always going to be something that you miss, because the world is very large and you are only one writer trying to finish your book some time before the heat death of the universe. And no matter how small the thing is that you get wrong, some of the people who read your book are going to care very deeply about it, and at least one of them will write you an angry letter, or flame you in their blog, or give you a bad review on Amazon. Pretty much the only thing you can do about it is resign yourself to the inevitable, and be gracious when it comes around.
That being said, there are a couple of things you want to try exceedingly hard to get right, because the people who care about them are even more passionate than the other people who will find errors in your stuff. One of those things is guns, and the other is horses. Horse people and gun people (who are usually two different sets) are on beyond passionate about their subjects — “fanatical” might be a good word. Your best bet, if you find yourself committed to a project that’s going to involve a lot of guns or horses or both, is to get yourself a gun expert or a horse expert, as needed, and consult with them frequently during writing and revision. The good thing about horse people and gun people is that they like to talk about their passion, and are usually happy to play instructor. (Don’t forget to thank them profusely in your acknowledgements. That way other horse and gun people will know that at least you tried. The same goes for any other people who may have been sources of professional expertise.)
And finally, research is distracting. At some point, no matter how fascinating the trail of breadcrumbs you’ve followed in search of some telling detail, you have to put the books back on the bookshelf and write.,