犹如在大海里捞针，这也许几分钟就能破解，或者是需要好几天。

Its a needle in a haystack and it can take a minute for the crack to be completed or maybe days.

youdao

小偷跑得很快，消失在地铁的人山人海里。警察要找他好像大海捞针一样。

The thief ran quickly and disappeared in a sea of faces in the subway, leaving the policeman with a job like finding a needle in a haystack.

youdao