But, it's not self-narration is it? The orc still attacks you. You're narrating why the orc didn't just cave in your skull with his club.
Any time you are narrating what your PC does, it's self narration. Nothing prevents the PC from saying, after he's hit by a blow, that he the character remains stalwart and unphased, or that he the character dodged nimbly aside so that the blow only glanced off doing minimal damage. Players are allowed to narrate that they are cool and awesome, especially when they are being cool and awesome.
It's not your success or failure that you're narrating. Not really. You're narrating the monster's failure to achieve whatever that monster is trying to do.
Sure, but the monster didn't fail. The monster the "hit". Your narrating how you mitigated the monster's success with your skill, or magical prowess, or divine favor, or simply being as tough as nails. I mean, as long as it's only color, I have no problem with a PC M-U narrating how he turned the blow aside with a spontaneous magical aura of protection, ending up with only a scratch. That's perfectly valid self-narration and its not breaking the rules in any way because what the rules determined to happen - the loss of 4 hit points - still happened. It's just color of the fiction, and in as much as color of the fiction is about the PC, the player is fully within his rights to use whatever color he wants. And that, in my opinion, applies to D&D in the RAW because D&D doesn't define contradicting process of play where only DMs are allowed to provide narration.
Again, at my table the following rule prevails - I won't provide color of fiction to your PC's thoughts, words, or actions (without their consent) and in turn the player will not add anything to the setting through of narration (without my consent).
And, sure, it's not really a choice, more of a HP tax on narration. You have to pay every time, you have no real choice in the matter. But, it's still YOU paying, not the DM telling you what happens. It makes the players active participants rather than simply receiving whatever the DM wants to dish out.
Sure, you could as a GM require all players to provide the color of fiction and to give narration after all fortune rolls. You don't need the concept of "spending" hit points to do that. You just simply tell the player to provide combat narration the same way you might tell a player to provide some dialogue if they are engaged in social role play. I just tend to prefer to leave combat narration voluntarily because there are plenty of occasions where combat narration becomes redundant and boring, and you are really for the moment trying to keep the focus of play on tactical wargaming so that the combat goes quickly and doesn't itself become redundant and boring. If something cool happens or the player is inspired, they can of course color the fiction. But I don't find it useful to force to do so.
I learned this from playing games were if you as a player provided color of fiction you were paid in a bonus on your action with bigger bonuses reserved to more creative color of fiction. That gives players a big incentive to provide creative color of fiction. But what I learned is that it didn't actually help the game to require every blow to be described in detail. And in retrospect, that's not surprising because few if any novelists bother to describe every blow in a fight either. The really fun thing that adds to a combat tends to be dialogue between the participants.
I have to admit, I can see a lot of things opening up if you head in this direction.
Give it a try and tell me how it works.
Contradictions rank so far down on the player's radar that, frankly, who cares?
