大海捞针 (大海撈針) dà​hǎi​lāo​zhēn
needle in a haystack idiom
To fish for a needle in the sea; to engage in a search that is virtually impossible or extremely difficult to succeed.

Finding a friend you haven't seen for years in this big city is like looking for a needle in a haystack.

Frequency

Written text
0.024 per million

Sources

Frequency data
BCC Corpus (BLCU)