cast pearls before swine idiom
把有价值的东西给不识货的人;明珠暗投，对牛弹琴
to offer something valuable or good to someone who does not know its value
I'm afraid you're casting pearls before swine with your good advice - he won't listen. 恐怕你给他忠告就好比对牛弹琴——他不会听的。