A needle in a haystack

Meaning

Something that is extremely difficult to find because it is hidden among a large number of other items. It suggests an exhaustive and nearly impossible search.

Frustrated, hopeless

Used in a sentence

• Finding my keys in this messy garage is like looking for a needle in a haystack.
• The witness is like a needle in a haystack in this big city.
• Looking for that specific screw is like finding a needle in a haystack.