The hunt for an essential item that IS already hard enough to find on its own, but ALSO in a situation with dire consequences if the wrong item is taken and/or the item isn't found in time.
Much more dangerous than the standard needle in a haystack.
"In front of you are one thousand buttons. One will disarm the nuke. All the others will set it off. You have five minutes."
"Agh, finding that button will be like finding the hay in the needle stack!"
(figure of speech) referring to something small that is difficult to find in a large space, it quite literally would be like searching for a needle in a haystack, obviously nigh impossible.
Finding your dick to take a piss must be like finding a needle in a haystack.