This idiom originates from the Zuo Zhuan (
左传), the ancient chronicle. Duke Jing of Jin fell ill, and two spirit children appeared in his dream saying they would hide 'between the fat (
膏) and the diaphragm (
肓)' — a place no needle or medicine could reach. The physician Huan diagnosed this and said the illness was incurable. Ever since,
膏肓 has meant the most inaccessible and critical inner region of the body, symbolizing hopeless illness or irredeemable situations.
