So you have some characters interacting in your game (I have no idea what the rest of the game looks like). you get to a point where two characters or two players want different things. To resolve these things, play goes like this:
- One of the two players declares two possible outcomes for the situation.
- The other one picks which outcome actually happens.
That's all. But I think this construction would be much more interesting in play than it is to describe.
Now, if both players have equal authority and opposed goals, you might need a rule "You don't specify who gets what". So if two PCs are fighting over an ancient holy relic, you could say "One of us gets the idol, but they also are horribly scarred in the process, OR
the idol is destroyed in the battle and no one gets it." But you can't say, like "I get the idol or
you get horribly scarred" because that would leave a crappy choice for the second player. Possibly the rule could even be amended to be "you declare as many outcomes as there are characters in the conflict, but the other player decides who each outcome applies to."
The thing that interests me here is that it would encourage mixed results in conflicts. Like a kid slicing a cake, you want to make the smaller half as big as possible, which pushes toward evenness in results. So you get pyrrhic or bittersweet victories or losses where you gain something. And those are good gaming material.
The other situation where this would work is if the players aren't in any way confrontational. I can imagine a game like The Court of the Empress
(or another game where one player's goal is to please the other player) that used a similar setup. The most benign of GM setups would be similar: the GM proposes two outcomes, and the player picks which one they want.
Actually, with a GM and a torturous game (a la My Life With Master or Paranoia) the GM offering two horrible fates for your PC and you having to pick which one happens could also be really cool.