画饼充饥
In the Three Kingdoms Period (220-280), the king of the Wei, Cao Rui, wanted to select a very capable man to work for him. He said to his ministers: 'When choosing a talented person, always beware of（小心，谨防） one with a false reputation. A false reputation is just like a picture of a cake; it can' t relieve（解除，减轻） hunger.'
Later, this idiom came to be used to mean comforting oneself with unrealistic（不切实际的） thoughts, without solving practical problems.