If we writers had to be an expert on everything we write about, we'd spend so much time on research that we'd never get anything written. The late Linda Shelley Whiting, a true historian, spent ten years researching the life of one man before she wrote a biography about him. If I'd taken the time to be that thorough, I'd still be working on my first historical novel.
I've said before that even though I've published four historical novels, I'm no a historian. Not even close. I love history. I love researching the past. But first and foremost, I'm a storyteller.
Whether you have a heavy amount of research in your story or not, chances are, your story will have elements you aren't 100% familiar with. It's your job to make sure those things ring true. A huge part of ringing true means getting into the head of your characters accurately, whether they're a different gender from you, from a different time period, or in a different occupation.
A tricky part: getting the small things right isn't always possible from reading up on a topic.
For example, if you're writing about a doctor, you'll need to know not only medicine but what it's like being that kind of doctor. No amount of reading medical literature will prepare you to write about what it feels like in the ER during a crisis. Only an ER doctor (or a nurse or an orderly) knows. Pick their brains.
Have a lawyer in your book? Better study up on life at a firm, and that means more than legal mumbo jumbo. It's the politics of who does what work, how hours are billed, what happens when clients don't pay, how often you really end up in court, who gets what bonus, the types of law firms out there and what kind your book needs, and more.
Is one of your characters living on a dairy farm? Find out what that means, in specifics: tools, schedules, sights, sounds, smells. Someone who grew up on a farm might mention that when they walked the barn in the morning, mice scurried into piles of hay. Chances are, that kind of detail would never occur to a city slicker.
It's easy to let our personal world lenses do the work because we don't know what we don't know.
Like the time I wrote a scene with male character talking too much like a woman. Fortunately, a male member of my critique group pointed it out so I could fix it. We then razzed him about having his female lead constantly trying to get big tangles out of her hair with nothing but a comb. (Women know she'd need a pick or a brush.)
Profession and gender are biggies, but think of other life roles as well. I was pulled out a novel once when a mother didn't bat an eye when a perfect stranger (a big, threatening man) took her baby and walked off. She simply followed along. My mommy radar went crazy. No way would a mom roll over and let that happen. Not when her baby is on the line. I found out later that the author isn't a parent. Eureka.
Pregnancy is another experience I've had that some writers get wrong because they haven't lived it. Reading about it isn't enough, so when they try to write about a pregnant character, they miss the nuances of what it's really like. (No, if she's 9 months along, she probably won't be hopping off her bed and racing down the stairs.)
On the other hand, I've never been a competitive swimmer. I've never performed surgery. I've never driven a tractor. I've never been a teenage boy. I've never raced bikes. I've never had cancer (knock on wood . . .).
That's not to say I can't write about those things; I can . . . provided I do my research not only into the surface-level facts, but into what the lens of that kind of person/experience would be.
One great way to do that is by interviewing someone who has experienced that element before you write about it. Ask open-ended questions (ones that cannot be answered with "yes" or "no"). They encourage the other person to talk and give detailed answers. Record everything; you never know what tiny detail will turn out to be golden.
It's also useful to have them read your work after you've drafted it. They'll notice behavioral, setting, and other details you either got wrong of simply left out because you didn't know to include it.
This method was the best thing I could have done with my last novel. Since its publication, I've had readers, who have experienced the very thing I was writing about, contact me to confirm that I'd been through it myself, because there was "no way" I could have portrayed it so well without experiencing it firsthand.
(It's moments like those that you do the happy dance.)
The book is fiction. I didn't retell the stories of the women I interviewed. But I did rely on them to help me see the world through a new lens so I could tell my characters' stories. Looking back, I can say confidently that there's no way I could have written the story with any semblance of success without help. I didn't have the right lens on my own.
Another one of my books features a horse prominently in the story. Going in, I knew little to nothing about horses. I did a bunch of research myself but eventually turned to a friend who grew up with horses. She helped map out a few plot points, spotted errors, and suggested some changes. After she finished looking over it, I made revisions and handed it to yet another expert, who caught a few more things.
When you give your work to a "lens" reader, ask them to keep an eye out for details and behaviors that don't quite work. You can give a partial list of things to watch out for, but make sure they know it's not comprehensive; you don't want them missing something big because they were looking for vocabulary and totally missed that a pilot would never assume such-and-such.
Using outside readers won't guarantee that you'll be 100% correct, but it sure ups your odds of nailing a character's inner workings so they seem truly alive to your readers.

