What is madness?
I'm not talking here about characters with a mental illness. Depression is technically a mental illness. (All right, it's a mental disorder, but you get the idea.) You feel sad with no actual reason; you don't say up at night painting the walls with honey so that the bees can hear you and sing your songs of praise to the bee-mother.
The relevant point is that this is big, dramatic madness, not the sort of thing that you add to a character after you've taken an Introduction to Psychology class. We're talking about characters who don't perceive reality in the same way as everyone else, characters whose fundamental ability to deal with the world is broken. They're not quirky, they're not funny, and they sure as heck aren't there to dance for the amusement of anyone else. These are characters that give you a skin-crawling sensation and a sense that something is very, very wrong here.
In other words, this is about cinematic insanity, not the ever-growing and important field of mental health. (If you have to be told not to use this stuff as a key to understanding real mental issues, I'm very disappointed.) Your character's mental disorders aren't under discussion, just the fact that he or she is now several cards short of a full deck.
Why do I want to use it?
For starters, madness provides an important function by giving other players a problem that they cannot punch out of. This is kind of a big deal because most MMOs take place in a setting where problems can be dealt with via weaponry, and player characters carry obscene amounts of weaponry. Giving players a problem that doesn't go away with a few determined rounds of combat is a major asset, and "the one person who knows something important is completely crazy" is certainly such a problem.
But there's also the very simple fact that William Shakespeare understood: Madness is dramatic. Mad characters lead allies on wild goose chases, cause harm to others more or less at random, and start rumors inadvertently. Plus, sometimes the maniac turns out to be completely right in the end, which is even more of a mind screw. A character with altered perceptions of the world makes for a lot of interesting conflict, provided that the character is used for conflict and not just wacky antics.
So how does it kick off?
I'm glad you asked, section header. Madness for dramatic purposes tends to have one of four sources mostly because the fact that "aberrant brain chemistry controllable via pharmaceuticals" is a really boring conclusion.
He hurts too much: There's a certain amount of loss that the human brain can cope with, but too much damage throws it into tumult. Get hit with enough trauma at high enough speed, and a mind might just shatter from the impact. Characters like this have been dealt a horrendous blow, either through tragedy or malicious torture, and as a result, they've broken off ties with reality altogether.
In most fiction, this is the sort of blow dealt to a character seen as being particularly solid, a sound mind in a sound body. Expect to have a character talking to dead friends, lost relatives, or even going from a titan of a man into a sniveling wreck within moments. It's not pleasant.
He knows something he shouldn't: Also known as Lovecraft Syndrome, this is when your character picked up more knowledge than he could handle. Maybe he learned some horrifying fundamental truths about the universe, maybe he found out his real father is someone awful, or maybe he just isn't prepared to deal with the truth of point nine repeating. The point is that he's become a babbling shell as a result.
Usually, this works best in a setting that allows for sanity-blasting revelations, but you can also do just as well in more benign settings by overfilling a character's head. Imagine if your character in Guild Wars 2 managed to absorb the entirety of all human knowledge over the past 200 years at once. He's going to go crazy because the human brain simply can't process that much information.
There's an external force: This reason is blessedly simple. Aaron has gone crazy because Ben used the Crazy Macguffin to make him crazy. Stop Ben, and Aaron goes back to normal. Or doesn't.
Technically, trauma counts as an external force, but here we're talking about a much more push-button madness. Some external set of circumstances is basically entirely behind everything, and removing those external circumstances either negates the condition or makes it curable.
He's just like that: In some cases, there's no reason to be found. The character is just plain mad. He might not have always been like that, but at this point, trying to untangle the path back to a reasonable human being is a fruitless endeavor. He's out of his mind, and the best you can do is cope with all the crazy.
Mad but north-northwest
I've got a lot more to say on this topic -- as it turns out, enough to put it into another column. I hope the anticipation doesn't drive you batty.
Feedback is welcome in the comments or via mail (firstname.lastname@example.org), just as always. Next week, I'm going to talk about the oddity of roleplaying with people who know you better than they know your avatar, and then I'll finish up the madness column.
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.