TO BUILD A FIRE
One major lesson that might be learned from the story; always be prepared and have a backup plan because nature is unforgiving.
This main character is a newcomer to the Yukon area. He seems arrogant yet ignorant in his approach to the wilderness by calling the old timer "womanish". He was relying on just witt and intelligence.
An example of what he needed to prepare for the wilderness would be for the main character to listen to the old timer who lived in this environment. He told him to never travel alone or in 50 below. This advice may have saved his life. At the end of the story, the character seemed consumed with regret, his reflection stated that he remembered the old timer's words.
Another example in the story to never knowing nature's harshness in the Yukon was given by the companion dog. The dog was reluctant to leave the fire in the freezing cold. The dog survives on instinct. Had the man been aware of the clues from the dog to stay infront of the fire he might have not gotten frostbite.
To summarise, I have concluded that the main characters lack of knowledge for his environment lead to his death. Not even intelligence can go against natures indifference.