Yes, well, I thought it odd that you started by saying that you aren't focusing too much on mechanics and then talk about nothing but mechanics and how they enable your characterization and how you couldn't successfully characterize without knowing the mechanical boundaries. I mean, yeah? Weird.That's a very odd way to categorize what I just said. Mechanics are simply boundaries for the characterization. Beyond that they play no role.
And, it completely doesn't address the point I initially made that you're too focused on mechanics, here. It's less about how the game does game stuff and more about what you're willing to put at stake. You're coming at it from the point of view of what you don't want at stake and then checking the mechanics to see if they do, indeed, protect these things -- if not, you adjust. I'm saying you can put anything at stake. Sure, the mechanics will influence how at stake things are, but you don't need permission -- which is what I'm saying. You're still asking for the system to give permission or to tell you that you can't protect your PC in some areas. That's too focused on the mechanics -- you've stepped in the right direction by recognizing that more can be at stake than just the health of your PC, but you're not across the line if you're still looking to game mechanics to tell if you such. Take your fighter example. You say you wouldn't play a fighter who's conception is that they can't be beaten in combat if the mechanics say you can. I'm wondering why not? Surely it's interesting to play a character that might fail to realize what they assumed was their core truth and now has to find a new way? Or, maybe, they actually don't lose in combat, and they are the badass (or stupid lucky) that they believe themselves to be! Risk more.