The price your antagonist pays without seeing it
Your antagonist's path costs them a specific human ability, and the difference between the two sides is not the size of the loss but whether anybody lets themselves look at it.
Under every strong story is an argument about how to live. In StoryDNA it starts with one human quality your story stands for, like honesty or courage, and the destructive quality it argues against.
The word you pick can be a simple one. What makes the story yours is what practicing that quality costs your protagonist, why your antagonist believes the other way is right, and what the world looks like when nobody pays the price. That's where your plot, your stakes and your ending come from.
Your antagonist's path costs them a specific human ability, and the difference between the two sides is not the size of the loss but whether anybody lets themselves look at it.
A destructive quality can be built into an institution, then into manners, then into the atmosphere of a place, while a decent one has to be performed by a named person every time.
A sacrifice only lands when the story has already named what happens if nobody makes it.
Your protagonist and your antagonist begin inside the same destructive habit, and what separates them is that one keeps paying for the decent thing while the other found a way to stop.
The sentence that lets your antagonist wield cruelty without guilt has a fixed form, one sentence in the first person with no irony in it, and writing it out is a task rather than a note.