“Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of the facts and evidence.”
A lot of aspiring writers (and all too many published ones) I've met have treated facts as a sort of irritant. The really good ones can fudge them with impunity, but often don't. The ones who can't get away with fudging them seem like they're trying to make Triple Chocolate With Marshmallows and Walnuts when just a basic fudge would more than do. Some of them don't even bother with fudge, and instead try to get away with fondue.
The fact is, you've got to be very careful indeed about fudging your facts. There's this thing about the Willing Suspension of Disbelief - it's willing. People become unwilling in a hurry if they have any reason to distrust you. The smoothest writing, the most gripping characters, the twistiest plot in the world might not save you if you blow a major fact. Even minor factual errors can work like repeated minor tremors on the mind of someone who's just moved alongside the San Andreas Fault - enough shaking, and they might decide not to wait around for the Big One.
Even if your readers decide to stick around, their Willing Suspension of Disbelief suffers. You don't want to kick them out of the story world by making them go look up the actual square root of 89,425 and say, "Hmm, thought that was wrong." Factual errors are like tiny pebbles in the shoes for a reader's mind. A minor irritant, yes, but the wearer will never feel quite the same about what they're wearing after too much discomfort. You want them living in your world with no more discomfort than what you've consciously and intentionally chosen to make them feel. You want them to trust you.
For those of you tempted to believe that the majority of your audience probably won't know or care when you've got something wrong, remember this: a few of your readers will know bullshit when they smell it. Such as, people who previously enjoyed your books until they found out what a lazy git you are. Such as, people who have never heard of you but would have become die-hard fans if the know-it-all had given you a thumb's up instead of the waggling thumb of doom. Such as, reviewers. Such as, those folks you're going to have to be polite to at signings. Such as, your editor/publisher/distributor. Such as... well, you've got a good imagination, you can carry on with this exercise if you're not convinced.
Then consider the fact that the advent of the internet means that your disgusted readers can tell absolutely everyone in the world just what a putz you are.
None of this may really affect your bottom line, but it just might, and it may certainly damage your readers' experience with your story. That's not something you want, is it?
So now that I've convinced you that facts are important, what to do?
These are facts that come from outside of your story. They can be anything: the firing rate of an AK-47, the growing of roses in temperate climates, why the sky is blue or why cats are insane. These are the facts some know-it-all reader is going to know and will have endless fun twisting your nose over if you get them wrong. The degree of nose-twisting increases in inverse proportion to the difficulty of verification - the easier something is to verify, the harder your nose will get twisted, and the more people there will be queuing up to do so. Take the following advice so your nose will not fall victim.
Get Them From More Than One Source
That is, first and foremost, the most important thing to do. Don't rely on a single source for the facts. Even the Encyclopedia. No matter how much you think you can trust your source, don't trust 'em. What's good for you in medicine is good for you here: always get a second opinion.
And don't get a referral to a second opinion provider from the original source, at least not until you've confirmed that they truly do know their business. After all, if the original source was in error, and they got their erroneous facts from another erroneous source, you're still going to end up with unfactual facts. Confirm your facts through an independent source whenever possible.
If you want a good example of why this is important, you don't need to look any further than Future War. The author relied on a single book by the bleeding defense attorney to get his facts about Ruby Ridge. Needless to say, he got all the facts wrong, including the easy-to-verify ones about who came out of that fiasco alive and who didn't. It's very, very hard to believe an author is an authority on any subject, even one in which he is ostensibly an expert, when he can't even get that much right. If he'd bothered to confirm with a third party, such as Wikipedia, he'd have saved himself a lot of embarrassment.
If I had known nothing about Ruby Ridge but wanted to use it in the background of a story, and had looked at the notes to find out where to go for more, all I'd have gotten is Gerry Spense's biased book, and the errors would have multiplied. Confirm any facts you intend to use with a third party. The more important the fact is to your story, the more you need to verify it.
Know Where Those Facts Came From
Col. Alexander's unfortunate experience trusting a defense attorney to tell him the truth about Ruby Ridge points up an unfortunate fact: sometimes, people twist facts or make them up entirely to serve their own ends. You've got to know the motives of those who are presenting you with the facts as they see them.
Neutrality is bliss. If you can find a neutral source, milk it. This is getting harder these days, but there are still a few around - people who have more stake in getting the facts right than in twisting them or obscuring them for their own ends. Some fields lend themselves to truth a little more readily than others. You can probably trust a mathematician - after all, anybody with a sufficiently strong calculator can verify his or her facts. Peer-reviewed and established science is generally safe. But in most cases, you're going to run into conflicts of interest.
So know the motives of those you're trusting as factual sources, and whenever possible, verify with people who have differing opinions. My personal belief is this: two people who despise each other and would happily disagree that a clear sunny sky is blue if they could get away with it will probably be telling the truth when they agree on a fact.
Get the facts from as many varied sources as possible: where the facts agree, they are more likely to be factual. Pay careful attention to credentials, though. Just because a whole bunch of diverse nut jobs believe vaccines cause autism doesn't make it true, for instance.
You can generally have a little more faith in someone who's spent their life immersed in research on a subject vs. the dabbler who thought it was interesting, read a few books, and then wrote their own. A little research on the Internet will tell you what the professionals think of your source, if you can't tell by the References. Get the buzz. Buzz is easy to come by these days, and it can keep you from swallowing the fibs of someone who likes to present himself as an expert but whom the true experts sneer at.
Whenever Possible, Talk to Someone Who Was There
You can read every book there is on war, but you won't really have a clue about it until you've either a) been there or b) listened to a lot of people who were. That's the case with most things. If you can talk to a real, live, experienced soul, do it. But only after you've done enough research on your own so you can understand what they're telling you and know what questions to ask.
If you want the facts about the job a policeman does, do a ride-along. If you want to know how old-fashioned candy's made, go to a candy store. For almost everything that can be encountered in the real world, there's either a way for you to do it yourself or get the facts about it from someone who's done it. Don't be afraid to reach out.
The other nice thing about reaching out is that your work can be vetted by experts who can fix nasty little errors before they earn you a painful nose-twisting. If your expert offers to read your book, tell them to let you have it with both barrels if you've screwed up. If you need to fudge something for dramatic effect, tell them. They can often help you fudge it believably well, so well it almost becomes fact.
If You Fudge a Fact, Make Sure It's Tasty Fudge
See above. Know what you're doing before you start twisting facts to fit your own nefarious purposes. You can't pile mud in front of someone and tell them it's Triple Chocolate Marshmallow Delight with Hazelnut Crème. They won't swallow it.
Get the flavors right, though, and they'll believe it's the real thing. And that's what the Willing Suspension of Disbelief is all about.
You've worked so hard on getting the external facts right that you may forget that internal facts are just as important. In fact. probably more.
This means keeping track of the facts of your story. If you've established that Bertha has blue eyes, you need to keep them blue. If they turn green without her putting in colored contact lenses on page 194, you've got troubles.
Make lists you can consult. Every time you establish a new fact about your world and the things and people in it, add those facts to the list. Brad is 6'4" on page 1. Write it down. Ten pages later, you find out he has a crooked front tooth and despises Plato. Write it down. That way, you don't end up with a 5'10" skinny dude with perfect teeth and a beloved volume of Plato at the end of the book.
Do this for all aspects of your created world. If you mention who ruled the place five thousand years ago, enter it on that world's time line. If you pop an island off the coast, make sure you've got it on your atlas. Readers are sensitive to these things. They'll get you if they find out the island moved down the coast six hundred miles and the ruler's name suddenly changed for no discernable reason. Too many mistakes like that, and it won't matter how many external facts you got bang-on, they're going to beat you over the head with your own book when they finally get a chance to meet you.
Or they'll ask embarrassing questions about the inconsistencies in public, which is even worse. Especially if your book was out in paperback. Physical pain lasts only so long. Public humiliation, like diamonds, can be forever.
Don't let it happen to you.