expression, i-adjective
once a fool, always a fool; a fool is only cured by death
Proverb meaning that a foolish person cannot change their nature; often used resignedly or critically. The literal sense is 'a fool won't be cured unless they die'.
彼はまた同じ失敗をした。馬鹿は死ななきゃ治らないって本当だね。
He made the same mistake again. It's true what they say: once a fool, always a fool.
No matter how many times I warn him, he doesn't change. A fool is only cured by death.