조인
Although Cao Ren behaved brashly and had no regard for laws when he was young, after he joined the military when he grew up, he started following rules and regulations strictly and he went by the book in everything he did. Once, when Cao Cao's son Cao Zhang was on away on a campaign against the Wuhuan, his brother Cao Pi wrote to him, "Shouldn't you follow rules and regulations in the same way Cao Ren does?"