In "To Build a Fire" Jack London's narrator observes that the man is "quick and alert," but he lacks imagination. And, so, he overlooks the significance of these things:
- The lack of sun casts a pall over the ground and keeps the day from warming.
- There are several feet of snow on top of ice and the wide Yukon river is hidden
- It is much colder than he has figured it to be.
Other mistakes in judgment prove fatal:
- He ignores the advice of the old-timer on Sulfur Creek, who has told him it is too cold, and who has said no man should venture out alone in such severe cold.
- He starts out on a nine-hour trek
- He underestimates the forces of nature. For example, his cheeks begin to freeze because of the severe cold that he has not measured accurately.
- He steps into the icy water under the snow by the river.
- The man makes the fatal mistake of building a fire to thaw out his foot under some snowy branches and the fire is put out by the melting snow.
It was really wonderful to read your question. No need even to review the story to mention the biggest mistakes that stand out in my mind. In my opinion, the absolute biggest mistake the man makes is NOT LISTENING to the Old Timer at Sulfur Creek. Here we have a character who is wise and experienced. Refusal to listen to such wisdom ends in death.
Yet another big mistake was to venture out ALONE. No adventurer should go solo. I don't care WHAT the weather is like. More recently, we have seen yet another man get stuck in a desert crevice and eventually have to CUT OFF HIS ARM to survive! The man in this story isn't so lucky! If there had just been a companion to the man as he set off on his journey, perhaps that companion would have noticed the tenuous ground, the stupidity of the fire placement, ... or any of the other dangers present along the way.
Next, I have to mention both the lack of pre-planning (not enough matches or an extra pair of socks?!?) as well as the lack of common sense (a fire under snowy branches? Really?!?). Regardless, these "mistakes" prove fatal for the man. A trek in the below-freezing Yukon just isn't worth it.
This man did not know cold. Possibly, all the generations of his ancestry had been ignorant of cold, of real cold, of cold 107 degrees below freezing point. But the dog knew; all its ancestry knew, and it had inherited the knowledge.
And here we have the last big mistake: not to pay attention to the creature ruled by instinct. When it is a question of survival, an animal ruled by instinct (whose evolution has depended on survival of the fittest) is the one to watch. Humans, of course, have some instinct, but are more about reasoning. In the story, it's this simple: the dog survives.