Which element best reflects the main external conflict of the story in to build a fire?

The main conflict of building a fire is that people usually don't know the correct rocks/stones to use to build the fire. If people have the correct rocks/stones, then they could face another challenge. That challenge would be rubbing the rocks/stones together hard enough to make a fire.

If you are referring to Jack London's short story, "To Build a Fire," the central conflict is very basic. Can the man survive the cold weather until he reaches camp? In other Words, can he outlast nature's fury?