What is the meaning of the life book in the eight-character fortune telling of birth?

Sui Dynasty's "Zhao Jun Ci": "My life is thin, and the gentleman's kindness is light." Tang Li Shangyin's poem "Belonging to a Disease": "Affectionate and true life is thin, and it is easy to be ileum." "Ancient and modern novels Chen Yushi cleverly investigates Jin Chai": "(Lu Gongzi) cries once and sighs once ... for some reason, just because he lives in poverty." The fifth chapter of A Dream of Red Mansions: "It's a pity that he was born in his wife's womb."