From the Introduction:
How does it work?
In The Oathbreakers, the society is built around laws called Oaths. Conflicts arise when Oaths are broken. As the Calamities threaten things the characters care about, they are drawn deeper into the conflicts, and the stakes rise. The more you invest into the plot, the more you can influence the ending of the story.
In The Oathbreakers, the characters are defined not by skills they have, but by things the character value, hate and stand for.
The character's successes and failures are a narrative tool: each player will get a chance to influence other character's fates as he sees fit.
Game mechanics don't decide consequences of your actions - dramatic considerations do.