劳而无功（勞而無功）　

◎ 劳而无功 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] 费了力气但没收到成效

与不可,强不能,告不知,谓之劳而无功。——《管子·形势》