ignorance is bliss
Proverb meaning that not knowing something can bring peace of mind. Often used when someone is happier unaware of a difficult truth. Compare with 知らぬが仏.
See also: 知らぬが仏 (しらぬがほとけ)
He's taking it easy, unaware of the company's crisis. Ignorance is bliss, huh.
Very similar proverb meaning 'not knowing is Buddha' — ignorance brings peace. 無知は幸福 is a more direct translation of the English 'ignorance is bliss' and may feel slightly more modern or Western-influenced.
A Japanese rendering of the English proverb 'ignorance is bliss,' using 無知 (ignorance) and 幸福 (happiness). The exact origin in Japanese is uncertain, but it is likely a calque from English.