Movie heroes are usually people who have ‘dealt with this before.’ They have the knowledge that helps them survive, and even save the day, where ordinary people wouldn’t have a clue – they know how to handle the bad guys, how to spot booby traps, where the monster’s weak points are, etc.
It’s fun to play someone like that in a game. That’s why game systems have things like knowledge skills: monster behavior, history, forensics – skills that effectively make PCs experts in things that the player doesn’t have any knowledge of.
The standard approach for handling knowledge skills is to have the player roll the knowledge skill, and if he succeeds, give him some canon knowledge about the situation.
So say you’re playing a detective. You want to know who might have known something about the killer. Your character has knowledge skills such as Investigation and Streetwise – you roll Streetwise, the GM consults his notes, and tells you that you find a lead that points to an old warehouse. Your character’s knowledge skill stands in place of knowledge you don’t have, and that your GM probably doesn’t have.
Now, this isn’t a bad approach, but there is one problem with it. Only the GM (or whatever published adventure he’s using) gets to decide where the lead leads to – and he’ll share that knowledge if the player rolls high enough. Thus what knowledge skills really do is award the player access to part of the GM’s notes.
In the GMG method, Knowledge skills award the player with a little bit of creative control. Let’s revisit the detective example. This time you say, “I want to go snoop around the docks.” Then you roll Streetwise. You roll high – and that means when you get to the docks, the GM’s going to have a juicy clue for you...
You see what I did there? I turned Streetwise from a knowledge skill into a Creative Control skill. Presumably a detective probably knows the “right” places to snoop around. So because your character knows what he’s dealing with, you get to make up the “right” way to deal with it. The GM doesn’t know – because I’m not the detective, you are!
So how’s this work if you’re the GM? Doesn’t it disrupt your storyline? Easy – you probably already know who the killer is, because you wrote the mystery. You might even know what some of the big clues are. Let’s say you planned one for them to find at the old warehouse – well, you just move it to the docks. Or let’s say your clue doesn’t fit well at the docks – so you decide to expand your mystery a little. What could have happened at the docks that touches on your mystery? A strange package that arrived a few days ago? Another murder? Player creativity got us some docks in our game – deciding what the PCs find there is where you get to be creative!
If the player rolled high, you might give the docks a really important clue that’s going to affect the rest of the campaign. Or if he rolled low, you just make it be a minor clue – even one that points back to the old warehouse.
Now notice, you’re not “making it easy” on the player – he didn’t choose “docks” because he wanted it to be easy, he chose docks because he wanted them to be in the story, is all. You’re giving him what he signed up for: the experience of playing a detective who hangs around docks a lot.
(You might recognize this kind of thinking from the “Always Gets Mixed Up With Princesses” trait in my characterization of Deathstalker.)
I argue that skills like Streetwise (and lots of other ‘knowledge’ skills as well) should be treated as Creative Control Skills – skills where a success lets the player define the game world a little. When you use a player’s ideas, you’re doing him a big favor (fulfilling whatever image he has of detectives), without having to change your notes much at all. A lot of it is in how you think about it too: his ideas are expanding your story, not getting in the way.