First off, this was totally, most non-egregiously hands down the most unprecedented story we've read so far. "To Build a Fire" is one of a kind, and was written extraordinarily. The totally excellent story opens with the protagonist, an unnamed man hiking, alone, halfway on a trek through Alaska, on his way to reconvene at a camp of other travelers. When the story opens, it's already seventy-five below zero (the unnamed man's spit freezes and cracks before it can hit the ground--a bad sign), and the man, despite his current, life-threatening circumstances, trudges on without a worry. In fact, "not a worry" aren't actually the right words--he doesn't think that he even has anything to worry about, because he doesn't believe that anything could ever happen to him. Yeah, not worrying is actually a good call, worrying definitely won't get you anywhere, but shutting your eyes to the reality of whats actually ahead of you--that's detrimental.
In addition, and arguably his fatal flaw, the man is totally ill prepared for the journey--for one he's trekking all by himself, alone, save for a wolf-dog, something that "the old-timer on Sulphur Creek" told him would be suicide. The only food he has is a bread biscuit soaked in bacon grease with slices of bacon cut in the middle, and other than some matches and chewing tobacco, that's all he carries, which wouldn't be so bad, except that deadly cold, seventy-five below, and he's way too confident to realize it.
In fact, regarding this, if I were asked who (or, appropriately, what) the antagonist was, I'd say that if not the sheer brutal negative degrees Fahrenheit, the antagonist would have to be the man's own sheer arrogance--he was so convinced of his own invincibility that he traveled on, into the wild, until he had no chance of actual survival (bogus!)--basically begging the elements to overtake him. In fact, if it didn't end up being the hidden stream of water which soaked his foot that killed him, it would have totally and egregiously been something else. In a way, he was also the antagonist too.
Jack London's "To Build a Fire" is most definitely a realist piece. In much the same way Bierce does with "An Occurrence at Owl Creek Bridge," London kills off his romantic with a fatal dose of reality. London also saturates "To Build a Fire" with details, told and explained with an extremely realist "to the point" style, with basically no emotional bias in the narrative, i.e. giving the reader everything they need to know, and letting them jump to their own conclusions as to the text's meaning and their own, totally individual emotional impact.
