In "To Build a Fire", London illustrates that awareness of your surroundings are necessary to survive. London describes the man at the start of the story as a unthinking and unconcerned figure amidst harsh conditions and because of his lack of critical thinking, he met an unfortunate end.
Advice should be listened to
London shows that instincts are important to listen to in the face of a dangerous or detrimental situation. The contrast between the man's lack of listening to instincts and the dog's natural instincts help convey that instincts increase survivability.
Humans cannot beat nature
London conveys that thoughtlessness has consenquences when the man has to light a fire for the second time. The first time, he brushed off his mistake by laughing at himself and expressing his overconfidence but the second time showed that in the end, he could not beat nature.
Survival is an instinct
London claims that advice should be listened to through the man's overconfidence leading to his death. When he was given advice to travel with another person, he chose to simply rely on himself and regretted it in the end.
London shows the power of nature while the man stuggles against its forces. Contrasting with the man's rapidly changing state, nature remained as a constant and overpowering force.
In "To Build a Fire", fire, one of the most primal needs for humans meant survival for the man and the dog. The man's failure to secure fire due to his lack of instincts lead to the man dying and the dog with instincts surviving.