勞而無功（勞而無功）　

◎ 勞而無功 láo’érwúgōng

[bay the moon;work hard but to no avail;accomplish little; fool‘s errand; milk the bull; preach to the winds wash a blackamor white] 費(fèi)了力氣但沒收到成效

與不可,強(qiáng)不能,告不知,謂之勞而無功。——《管子·形勢(shì)》