I think that varies by game mechanic. I am not sure what that may be in Burning Wheel, which seems to be pemerton's primary game, but in Dungeon World and other Powered By the Apocalypse games, there is a set mechanic. Roll 2d6, add your relevant skill or modifier, and if you get a 10+ you succeed, a 7 to 9 you partially succeed or succeed but face some complication, and on a 6 or lower you fail.
So the game has a mechanic that does not rely on the GM to make a judgment call on how difficult a task would be and then set that as a target number or DC, as is done in most versions of D&D and similar games. Instead, the only variables are the PC's skill or ability that is pertinent to the task at hand, and the random die roll.
I am guessing that Burning Wheel and Cortex+ and the other games pemerton tends to cite are similarly designed. I'm sure he's shared how they work at some point, but I don't recall.
So this playstyle only really works for games specifically designed for it... that's interesting.
EDIT: To further expound I know he often cites the Marvel Heroic rpg and in that there are a couple of things you can do with the Doom Pool that definitely affect player agency (specifically as [MENTION=42582]pemerton[/MENTION] defines it) listed below.
*To use any affect that normally costs a Plot Point.
*Use special effects (SFX) that cost doom dice to activate.
*Split a hero off from other heroes or force them together.
*Activate a Hero's Limit. But first offer to pay them 1 PP instead.
*Create a new Scene Distinction (costs a D8 or higher). Anyonemay use this Distinction instead of their own Distinctions.
*To have a Villain interrupt the Action Order.
*Activate Scene or Event effects.
*Spend 2D12 to end a scene immediately. If the Heroes wereclose to winning, ask them to describe how they get most ofwhat they want and then present them with a tough choice,you win but X happens or at Y cost. If the Heroes were notclose to winning, ask them to describe how they lost or whatthey had to sacrifice (something significant) to win.
Now I understand he has an issue with secret backstory but honestly most of these effects you can create with the Doom Pool in the MH game seem to tread on the type of player agency he is advocating for... Create a new scene distinction, Ending a scene immediately, Split a hero off or force him to join up with the group... how do these not step all over the type of agency he is advocating for? Is it ok because they aren't secret backstory? Or is the infringement upon agency (regardless of it's source) really the issue...