Mistakes fail in their mission of helping the person who blames them on the other fellow.

The line treats mistakes as potentially instructive events—“missions” that can improve character and judgment—but only if the person who made them accepts responsibility. By blaming “the other fellow,” the speaker turns error into mere grievance, forfeiting the self-knowledge and behavioral correction that failure can provide. The aphorism thus aligns with a pragmatic, self-help ethic common in early twentieth-century American moral writing: progress depends less on avoiding mistakes than on owning them, learning from them, and changing course. It also implies a social dimension: scapegoating corrodes trust and blocks honest appraisal, while accountability enables growth.