The old timer was trying to convey the idea that the tiniest mistake will be the man's last because the weather gets so cold that death is not only possible, but actually probable, if the man is not careful. Think about the way this narrative progresses. Practically every paragraph has an instance of foreshadowing and the man continually thinks about his mistakes but continues his trak toward the camp site. He actually realizes, almost from the beginning of the story, that he has made some grievous mistakes.
This is foreshadowing on the part of the author and sets the tone for the series of mistakes that the man perpetuates.