good advice may be hard to take; good medicine tastes bitter
Proverb meaning that honest, helpful criticism or advice can be unpleasant to hear, just as effective medicine often tastes bitter.
His advice was harsh, but as they say, good medicine tastes bitter, so I accepted it honestly.
From the classical Chinese maxim 良薬苦於口而利於病, recorded in 『孔子家語』: good medicine is bitter in the mouth but beneficial for illness.