Stack：干草堆；Something that is extremely difficult to find. Anything that's on the verge of being impossible.很难找到的东西，也就是大海捞针；
Today, this phrase is typically said as "It's like trying to find a needle in a haystack." 现在，这个词组更多地说法是It's like trying to find a needle in a haystack. This is considered to be an extremely difficult thing to do, and rightly so.这被认为是很难做到事情。 Finding a tiny needle in a big stack of hay, while not impossible, would take a considerable amount of time and effort.也不是说不可能，但干草堆里找针需要花费很大的精力和时间。 Hence, when people are having trouble finding things in modern times, they often say this phrase to indicate the difficulties they are having.因此，当人们很难找到某种东西的时候，他们通常会用到这个词组去描述。
As for where the phrase originates from, I don't think it's entirely clear. 关于这个词组的来源具体不是很清楚。My guess would be farmers because I imagine them working with stacks of hay the most out of anyone. 不过合理的猜想应该是这个词组与农民有关，因为他们经常在和干草堆打交道。Here's what is known: 根据记载，This phrase is written in a old book titled The Complete Works of Washington Irving, published in 1834. 这个词组被用在一本名叫The Complete Works of Washington Irving 出版于1834年的古书里面。其中写道：
"If I want to find any particular article, it is, in the language of an humble but expressive saying, -- 'looking for a needle in a haystack.'"意思就是：如果我想找一个谦逊但又有表现力的句子的话，那就可以用大海捞针来形容。
1. Searching for my keys in the garden is like trying to find a needle in a haystack.
2. He tried to find his lost contact lens on the beach, but it was like looking for a needle in a haystack.