What is the central idea in "To Build a Fire?"
The central theme is most likely the conflict between man and nature along with a nice side theme of the dangers of ignorance. But, in this case, it is the man's ignorance and inability to respect the power of nature that leads to his downfall. The fact that the man has repeated warnings both from nature itself represented by the weather and the dog and from other humans aand ignores them is important, going along with many of Jack London's stories in emphasizing the importance of respecting nature and taking the right precautions.
A secondary theme has to do with the man being forced to come to terms with his own death, in this case at the hands of nature. He fights it for a while, but in the end must accept it and does.