Consider the possible basic conflicts in fiction:  man against environment, man against man, man against society, and man against self.  In most plots the conflicts are between people.  Even in Robinson Caruso and Castaway, tales of man surviving in isolation, other people are part of the conflict. The fact that the protagonist  learned to survive  on his own didn’t bring either story to an end. When people arrived on Robinson’s Caruso’s island, they weren’t friendly. The enemy had to be defeated. In Castaway the  biggest conflict occurred when the main character returned to civilization only to realize that the love of his life had married someone else. Contact with people only brought new conflicts.

What causes the conflict between fictional characters is often over simplified. Typically character A and character B want the same thing, but they don’t want to share. This love triangle plot is played over and over…