It makes a difference whose ox is gored.

The proverb means that people’s sense of justice often depends on self-interest: an injury or injustice feels urgent when it harms “our side,” but seems tolerable or abstract when it harms someone else. In polemical religious and political contexts—such as those surrounding the Reformation—the saying neatly captures how factions can excuse the same behavior they condemn in opponents. Attributing it to Martin Luther suggests a moral critique of hypocrisy and partiality, though the line itself reads like a long-circulating folk proverb rather than a distinctive theological formulation.