expression
the husband is always the last to know
Proverb meaning that a husband is often unaware of his wife's infidelity while others know. Used idiomatically to describe a situation where someone is oblivious to something obvious to everyone else.
近所の人はみんな知っているのに、彼だけが気づいていない。まさに「知らぬは亭主ばかりなり」だ。
Everyone in the neighborhood knows, but he's the only one who hasn't noticed. It's exactly a case of 'the husband is always the last to know.'
A traditional Japanese proverb. The exact origin is uncertain, but it reflects a common cultural trope about marital infidelity.