When something is very difficult to find it is like looking for a needle in a haystack. Especially because the area you have to search is too large and because of everything around it. We also say trying to find a needle in a haystack.
Hay is grass which is cut, dried and used as animal food or as covering material.
A haystack is a large tall pile of hay in a field.
"I went into my younger brother's bedroom to get the CD I lent him. It was like looking for a needle in a haystack. His room is so untidy."
"I tried to find my lost key on the sandy beach, but it was like trying to find a needle in a haystack."
The idiom was also used in one of my favourite songs, "Living for the City", a 1973 hit single by Stevie Wonder.
"Her brother's smart he's got more sense than many
His patience's long but soon he won't have any
To find a job is like a haystack needle
Cause where he lives they don't use colored people
Living just enough, just enough for the city..."
Now write your own example sentences: