What is a realistic challenge? If we're harmonizing agenda here, in the scope of what I said, then we need to identify and harmonize some version of "I want to experience the fiction for the sake of the fiction" and "I want to engage in a challenge I can leverage my skill to win." So, this sounds, at first blush, like it's trivial, right? But let's look at an example -- say 5e combat. We can do challenge, sure, but there's almost no fiction generated by the combat engine. The fiction only comes in with conditions and when creatures lose all their hitpoints and with some positioning and stuff. But we're not experiencing, really, the fiction of combat from the system because it's pretty thin on details of hits and damage and things. So, we "harmonize" and provide some flavor and details, and describe that hit as being stabbed in the leg. Sure, now we have fiction to experience, but then this nearly immediately gets challenged by the system as the PCs take a short rest, burn a hit die, and suddenly that stab wound in the leg is, well, not there? Ouch, experiencing the fiction is taking one in the face!
So, then, how can we harmonize? We toggle. In a given moment in 5e, we're concerned about the fiction, so we do that, but then we discard that fiction when we need to worry about the challenge part. And vice versa. It's not harmonizing, it's switching back and forth as needed. Hitpoints are so not about experiencing the fiction that anything that touches them becomes fraught from that lens. However, many of us have decades of experience in doing exactly this kind of toggle and most of those have never really thought much about it, so you get ideas that this is how it is, it's a harmonious whole, and it's perfectly easy to mesh these things. But, it's not, we toggle and don't notice. If you do not believe this, start another thread about hitpoints and see the argument between gamism and simulationism brought straight to the front.