cast pearls before swine

to offer something valuable or good to someone who does not know its value

把有价值的东西给不识货的人;明珠暗投，对牛弹琴

这个表达出自《圣经》。在这部分圣经中，耶稣给出了以下话语。

Do not give what is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet, and turn and tear you in pieces.

不可把圣物给狗;也不要把你们的珍珠丢在猪前，恐怕他们把珍珠踩在脚下，转过来再把你们撕碎。

这就是说不要与那些会滥用它的人分享你宝贵的东西。

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。