A very honest man--scrupulously so--encounters a ruthless brute.
The ruthless man brutalizes the honest one, who is fragile and over-reacts: he breaks down.
The honest man's reaction is so painful that the brute feels ashamed and tries to assuage the man he's hurt.
But the victim rebuffs him and won't be consoled. And so the brute feels some small degree of shame--a new emotion for him.
Later, the honest man finds an opportunity to harm the brute. It requires doing something unethical--a very small wrong indeed--but he takes the action, even against his own better judgment.
This disrupt the honest man's life. He goes off-kilter. All his habits are disrupted. He cannot maintain his ordinary equilibrium. The very orderliness of his existence has been endangered.
Slowly the honest man recovers his dignity. But he finds a small opportunity to abase himself--when no one's looking. Then he goes back to normal.
Meanwhile, the brute has become obsessed with a rather plain woman whom he had ignored in the past. He shows all signs of being in love with her.
But when he holds her in his arms and makes love to her, he closes his eyes he sees before him the face of the poor honest soul whom he harmed so callously.
--E. R. O'Neill