吃不到葡萄说葡萄酸
[chī bù dào pú táo shuō pú táo suān]
An idiom translating to 'Saying grapes are sour because they can't be reached/ eaten,' derived from the story of 'The Fox and the Grapes.' It describes someone who belittles what they cannot have or achieve, projecting their own shortcomings as inferiority in external objects or people.