Mark CMG
Creative Mountain Games
Right.
The character attempts to chop off the opponent's head.
In game A, where decapitation is an action that can be declared at any time, the player rolls the die and consults the mechanics to determine success.
In a game B, where decapitation is an action that requires expenditure of a meta-resource, the player decides whether or not to do so, and - if he chooses to spend the Daily power, for example - rolls the die and consults the mechanics to determine success.
If you're running game A, you need one narrative that accounts for failure to chop off the head (because the die rolled badly), and one that accounts for success (because the die rolled well).
If you're running game B, you need one narrative that accounts for failure to chop off the head (because the die rolled badly, or because the resource was not expended), and one that accounts for success (because the resource was expended, and the die rolled well).
Either way, the stories are the same.
The difference is that in game B, the player might realise in advance that failure to chop off the head is guaranteed (since he cannot or elects not to spend the resource)... so the narrative detail explaining the failure can be introduced prior to the die roll. Or, alternatively, the narrative detail explaining why it's pointless to attempt to chop off the head can be introduced, and he can attempt something else with his action.
If another player on the next turn decides to do some head-chopping of his own, his narrative should incorporate the already-introduced details, and might also explain why it's not automatically futile for him to try what the first player failed at.
The difference being that, as I have made clear, I disagree with an approach that expresses an action that can be attempted like tripping as an effect that can only happen once daily regardless of the actual circumstances that might exist and then adjusting the narrative to account for limiting the circumstances based on the mechanic that has created a foregone conclusion. This is beginning to look like a microcosm of the debate between sandbox play and GM plot-driven adventures.