Antagonism

The principle of antagonism: A protagonist and his story can only be as intellectually fascinating and emotionally compelling as the forces of antagonism make them. Robert McKee in "Story."

The antagonist is the force that comes against the protagonist and tries to stop what the protagonist is doing or trying to do. In characterization, the obstacles that the protagonist has to overcome help to expose the true character of the protagonist. Human nature is mostly conservative. We're all prone to "doing it the easy way." Providing conflict through antagonism adds depth to a story. The more powerful the forces of antagonism opposing the character, the more completely realized the story and character must become. Pouring energy into the negative side of the story won't just bring the protagonist and other characters to full realization, but also take the story to a powerful and fulfilling climax.

Antagonism doesn't necessarily have to be a character. There are many other sources of antagonistic power to befall your protagonist.

Experiment with forces of antagonism in your story. Remember to make it probable and believable.