We can accept a book about vampires. Or how about a search for Atlantis? Or better yet, the Holy Grail? From Dracula to dinosaurs, we don't mind reading these books. We take them at face value.
But what we can't accept is poor research into the real world. You'd better know your stuff, and make it believable.
It's true. Details matter. Time and again writers who know their area of expertise will find readers who appreciate their knowledge. But if you stray into unknown waters, you had better get your facts straight.
In Clive Cussler's Trojan Odyssey, a hurricane is spotted forming out in the ocean. And guess what? The person who discovered it gets to name it. Wait, what? That's not correct. Every future hurricane for years to come has a pre-assigned name, and we can all look that up on the National Hurricane Center's website, part of the National Oceanographic and Atmospheric Administration. So when we read that in a Clive Cussler book, it leaves us scratching our heads. A prolific author, he's no stranger to oceanographic goings-on.
The idea is the reader will accept your world if you make it believable. All things must be accurate. Tell us a kid finds dragon eggs, uses a magic spell on them, and they hatch. Fine. But if you then tell us the kid's father drove up in a classic 1961 Ford Mustang convertible, we throw the book at the wall in frustration. There is no 1961 Mustang. Okay, I made that example up to demonstrate the point. The old saying "write what you know" can be applied for different reasons. If it's not something you're familiar with, either do your research on the details or leave it out of the story.
When J.R.R. Tolkien wrote The Hobbit and The Lord of the Rings, he first created an entire Elvish language. All Elvish spoken was accurate to how he had created it. That's the kind of dedication that makes fantasy acceptable. And it applies to science fiction as well. When writers would attempt to create a new Star Trek episode, they were held to stringent guidelines. There was a list of characters, each completely defined in personality, appearance, etc. There were specific alien races, exact descriptions of relationships between those races, and heavily evolved languages used throughout the series. One cannot simply ignore those details. The success of the Star Trek series and the Tolkien mythologies is a testament to following those guidelines and giving the readers wonderful stories and adventures within the defined limits of what can be expected.
Dan Brown's fifth book (possibly his last), The Lost Symbol, left people bewildered when he had CIA operatives investigating homeland security matters within the U.S. That's the jurisdiction of the FBI. Perhaps some people don't know that, but people who read those kinds of books usually do know that. Those details can kill the believability of a story, even when outlandish plots and fantastic events don't.
As I continue rewriting my own book that takes place on the coast of Maine, I have researched a variety of details including the topography of the land, the times for sunrise and sunsets in mid-summer, and even the average salaries of people living in smaller towns and what are their main sources of income. I've also visited that specific area a few times and spoken with the locals, and stayed in the kinds of inns included in this story. In fact, I even researched the accents.
I promise to do my best, to do my duty, to do my job as a writer and get the details right.
Suspend belief, that's the reader's job. Make that possible, that's the writer's job.