Let's get inaccurate
As I said in the opening paragraph, there are two kinds of delusion. The first is unconsciously imposed from the people you're around. If you grow up as a human in Ebonhawk in Guild Wars 2, you grow up being told that the Charr are evil. Odds are good that any evidence to countermand that statement will be met with indignity and refusal because you know full well that the Charr are evil and everything else is a plot to get you to trust them. Odds are you consider yourself smarter for not trusting them.
The other kind is self-created, and it's this one that I find a little more interesting. Things you grow up with are pretty much a matter of backstory, but things you refuse to believe are choices you make in the present that can have long-term effects. I used a humorous example up above, but this is something that can be played for drama just as easily. A husband hears that his wife died in battle and he refuses to believe it, insisting she's still alive. A woman is told her real father is someone she loathes and she refuses to accept it. Heck, this could include just being a member of a group and refusing to acknowledge anything going on that runs counter to the group's ideals.
Every so often, of course, you're right to not believe. But that's the exception. More often there will be things that our characters genuinely believe that they know to be objectively false either because the truth is too painful to face or because honestly processing the information would mean questioning a whole lot more beliefs. Let's look at each in turn.
I reject your painful truth in favor of my more pleasant one
The truth can hurt. A lot. Maybe your Sith in Star Wars: The Old Republic has found out that his parents didn't die an honorable death in battle against a Jedi but were in fact executed after fleeing the battle before a shot had been fired. It's the sort of thing that hurts on a deeply personal level, a fact that messes with your whole image of self-worth and what you should be doing with your life.
Here is where you most often find people who insist that the truth is a lie, that records were falsified or people were bribed or something else has been done to make it look like X is really Y. That, in turns, leads to a character seeking evidence to prove why this is wrong, despite the fact that the character is often well aware this evidence doesn't exist.
Ultimately, this is a better underscore for tragedy than anything. Characters like this are chasing an enemy that doesn't exist because it's easier to deal with that enemy than with the reality of the situation. It's the sort of thing that can lead to some great character development down the line if you play it right. Make a point of the character's goals, of how he or she wants so badly for this to be true that any evidence pointing to it being true will be seized upon.
Not coincidentally, finding indisputable evidence of the exact opposite is the sort of thing that can drive a character to madness. You'd spent so much time insisting that something must be true that when you finally can't avoid it any longer, you might be forced to grow... or you might just fold inward and break from reality altogether.
This is not my beautiful wife
Some truths are painful mostly because they mean you were wrong. Let's jump back to Guild Wars 2 for an example: Completing the story mode of the Ascalonian Catacombs suggests that the drawn-out war against the Charr involved much more failure on the part of the human spirit than most humans would like to admit. So your character could face that truth... or he could simply choose to dismiss these facts as lies spread by ancient enemies.
After all, if the version of events told by the Charr is true, then the conflict was one not of horrible invaders fighting a pure and noble nation but of two sides whose hatred for one another drowned out any voices of reason. That would mean that everything you had grown up knowing about the Charr was suspect, that all of the values you held so dearly were tarnished. It might even mean that the Searing itself could be looked at as something other than an atrocity, that it could even be an atrocity committed by a desperate people. Much easier to simply insist that you were right in the first place, and contradictions to that are just an elaborate fiction.
You see this publicly in the real world more often than not. It's especially frequent in people predicting the end of the world -- when the date comes and goes and nothing happens, you get public denials that the previous date was the real date or the day suddenly shifts to a later point or something of the sort. Expect this on December 22nd, for example.
This sort of voluntary denial is usually immune to being presented with more truth; what has to change are the character's underlying assumptions. Often the character in question is less aware that he or she is willingly blocking out reality as a result; she knows that there's a litany of facts, for instance, but she doesn't acknowledge how weak her dismissals really are. It's a key element in making a character whose perceptions don't line up with objective fact due solely to personal bias, however.
Keeping it unreal
No matter which route your characters go, the important thing is that just because you know everything about the setting doesn't mean your characters do. You're able to take the perspective necessary to see a more balanced side of conflicts, but your characters are knee-deep in events and may have access to only some of the facts, not counting the ones being willfully discarded.
Be a little ignorant. As we all are in real life.
Feedback is welcome in the comments below or by mail to email@example.com, just as in every other week. Next week, I'm going to talk about playing the same character time and again and what can be learned from that one character instead of a set of new avatars.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did.