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 again with competition not necessarily for the affection of a person but for a coveted prize, a position of power, or a piece of land handed down by the family. However, there needs to be another conflict, one of personality which keeps the two characters from doing the smart thing and compromising to work out this difficulty.
Personality conflicts are played out in real life frequently. One person is emotional, but sensitive and the other logical, but cold. One person is quick to take offense when another offers criticism, but the critique is really meant to help. A subtle war starts because one person perceives that another is getting the special privileges, which very well maybe true because people who treat others equitably are very rare. So a collision of characters can often be drawn from simply watching people around you.
In fiction authors often play heavy favorites with characters, creating heroes with admirable qualities and villains that are evil simply because they are. However, intriguing antagonists have real personalities that cause them to want to block the hero from reaching the goal.
Creating memorable conflict between characters requires requires an understanding of modus operandi or MO. MOs don’t just belong to criminals. They belong to everyone. These are the methods characters use to get what they want. If two clashing characters want the same thing, how they go about obtaining it separates them. This gives clues into internal motivations so authors do not have to blatantly describe characters as “good” or “bad.” Modeling characters on real personality conflicts results in heroes and villains whose life like immediacy draws the reader’s interest. The conflict in which neither one is the shining knight or the dragon is much more compelling.