Bill Zebub
“It’s probably Matt Mercer’s fault.”
Have you ever felt your hands sweat and your heart stop as you make a crucial roll, the one that will determine whether or not the whole party will be wiped out or instead whether your PC, the last one standing, will take down the last foe before they get to act and take you down?
At least in my experience, that's one source of excitement in RPGing. It would be different, and probably not as exciting, if I or another participant just got to decide you win.
Now imagine the same thing when, playing @Oofta's Mr B, you proceed to carry out your vengeance on the person with the necklace your daughter once wore. Where the exciting question isn't can I kill him? - Mr B is a mighty vengeance paladin, while this person with the necklace is just a commoner who was once a lowlife thug - but can I bring myself to do it? You've been building up your Steel by deliberately putting yourself into situations that inure you to shock and gore and viciousness (which is how Steel increases in BW). But have you got what it takes, here and now?
For me, at least, that's what it's about.
Hmmm...nope. Not feeling it. Can't really imagine feeling the same kind tension in the scenario you describe.
I can easily imagine the tension behind a critical roll (no pun intended) where if I hit with my sword we (probably) live, and I miss we (probably) die.
But if preceding that roll I have to make a roll to see if I can "steel" myself to do it I think I would just see that as yanking me out of the story because it's not really my character after all. Or, at least, I'm not inhabiting that character, I'm just controlling it. And only tenuously at that. So for me the tension would dissolve because I'm no longer 'there' in the story. (In other words, the attempt at performative roleplaying has come at the cost of experiential roleplaying.)
It may be that I just can't get my head around because after four decades of RPGing I just think an essential part of the experience is that those kinds of decisions belong to the player. Maybe I could get used to it. Maybe I could also get used to eating those black fermented eggs that are a delicacy in China.
But it's hard to imagine.