bù不notdé得obtainér而andzhī知know
Cannot be known; will never know.
Literal meaning
not (不) — obtain (得) — and (而) — know (知)
Origin
A classical four-character phrase indicating something unknowable.
Examples
Tā他wèi为shén什me么zhè这me样zuò做，wǒ我men们bù不dé得ér而zhī知。
Why he did this, we will never know.
Shì事qíng情de的zhēn真xiàng相rú如hé何，zhì至jīn今bù不dé得ér而zhī知。
The truth of the matter, to this day, remains unknown.
Usage & nuances
Used to express uncertainty or lack of information about something.
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