Imagine that you’re robbing a train, like a Wild West bandito. You’ve ridden your horse to the caboose and hopped on board, and now you’re up on the roof. Your goal is the engine, so you start moving forward. Each car is roughly the same as every other - same roof, same length to cross, and so forth. But some trains are harder to rob than others, and one reason for that is because there’s more cars.
Any given 2d6 roll is going to go 10+, or 7-9, or 6 or under, on more or less the same odds. Your stats peak around +2, +1 ongoing is awesome, and so forth. Every given roll is going to be fairly random. But how many rolls you introduce - and for what - can dramatically alter the feelings you get from the overall experience. Read A 16 HP Dragon for an example of this principle in action.
“How many in the air?” “Thirteen, sir.” “How many can I carry?” “Four, sir.”
This Iron Man 3 clip starts off a scene in which Tony Stark needs to rescue more people than he can really handle. There’s tension at every moment - coming up with a plan that’s going to fail, discarding it and trying another, keeping his charges calm, all with the ground rapidly rushing at everyone.
The argument in favor of modeling tension mechanically, rather than having the GM just add more boxcars to the train, is that fiction suggests that desperate actions succeed more often in higher-tension situations. The Discworld books sum this up with the adage “a Million-to-one chance succeeds nine times out of ten.”
Alright then - we have a gauge, called “Tension”, and certain things will increase it.
I want PCs to rise to the challenge of overcoming a crisis. But I also want the possibility that a PC falls too deeply into whatever feelings make them effective. The disillusioned swordsman wanting to give up, the kind princess feeling she’s unable to help, the plucky comic relief being unable to get a laugh.
So we’re going to introduce something called “Heart Armor”. The more of it you have, the fewer special moves are available to you, because you aren’t as emotionally invested in the situation and hence aren’t as motivated to help stop it. But the more Armor you give up - the more you allow the situation to affect you and bring out your own feelings, positive or negative - the more vulnerable you become to finally losing your composure or determination or restraint, or whatever keeps you able to solve problems.
Shedding your armor - revealing yourself - unlocks your moves. If you allow yourself to feel and connect, you can try to change the situation for the better. But don’t give too much of yourself away.
PCs will be differentiated by the moves that they choose, and those moves will correspond to their identity (who they see themselves as), their experiences (what they’ve seen and done), their ideals (what they’ll fight for, or against), and their sacrifices (the things they’ve lost, or given up, and the strengths that came from that loss). I’m still working out the specifics here.
I’m turning over the idea of “advancement through introducing backstory”. For example, imagine that you start with one Identity, one Ideal, and one Experience. You have 2 Heart Armor for being a PC, plus 1 more for each of these things, for a total of 5. Later, as you reveal more about your PC - what you really feel inside, losses you didn’t talk about with the others, or whatever - you gain a new Sacrifice or Ideal or whatever, and your Heart Armor rises to match.