What is the origin of the idiom "needle in a haystack" and when to use it?

The idiom "needle in a haystack" dates back to the 16th century and has been used in English literature since then. Its origin is quite literal, referring to the extreme difficulty of finding a tiny object (a needle) within a vast pile of straw or hay. This expression is often used to describe an exceedingly challenging or nearly impossible task of finding or locating something due to its extreme rarity, obscurity, or hidden nature.