es kann nicht sein, was nicht sein darf
proverb[əs ˈkan nɪçt ˌzaɪ̯n vas ˌnɪçt zaɪ̯n ˈdaʁf]
people find it extremely hard to accept facts when they go against their firmly held conviction or are otherwise devastating to them
es kann nicht sein, was nicht sein darf is a German proverb meaning “people find it extremely hard to accept facts when they go against their firmly held conviction or are otherwise devastating to them”.