The main problem with relying on nature to start a flame was that Fire was likely hard to find, requiring a "long journey and a deal of trouble."
Explanation:
It is stated in the paragraph that the man depended of nature to gather fire and this was only in places near volcanos or by the stroke of lightning, this made it hard to get, and they also needed to walk long distances to get to this places and protect the fire all the way back home so it did not die in the journey.
