It is difficult to paint the skin of a tiger, but it is difficult to paint the bones of a tiger.
Source: Yuan·Shang Zhongxian's "Single Whip to Seize the Tree", the second chapter: "Brother, you know people, know faces, but don't know the heart. You are of the same mind. How could he betray Liu Wuzhou and surrender to me? "Come on." "Zengguang Xianwen": "It's difficult to paint the skin of a tiger. You know the face but not the heart." For example, Sister Feng deliberately put her foot down. Seeing him go away, she thought to herself: "This is the time." It's '~'.
Are there such beastly people out there? "(Chapter 11 of "A Dream of Red Mansions" by Cao Xueqin of the Qing Dynasty)