There's no cure for stupidity; some people are so foolish that nothing will change them.
何度も説明したが聞こうとしない。馬鹿につける薬はないとはこのことだ。
I explained it many times but he wouldn't listen. This is what they mean by 'there's no cure for stupidity.'
彼の頑固さには手を焼く。正直、馬鹿につける薬はないよ。
His stubbornness is exasperating. Honestly, there's no cure for foolishness.
失敗を何度繰り返しても同じことをする同僚に、つい『馬鹿につける薬はないね』と言った。
I ended up saying 'there's no cure for stupidity' to a colleague who repeated the same mistakes.