英語候補it takes a thief to catch a thiefit takes one to know onethe wolf knows what the ill beast thinks
知らぬは亭主ばかりなりしらぬはていしゅばかりなり慣用句ことわざeveryone knows of the wife's infidelity but the cuckolded husbandthe husband is always the last to know
知る者は言わず言う者は知らずしるものはいわずいうものはしらずことわざhe who knows, does not speak; he who speaks, does not knowthose who know do not talk; those who talk do not know