This allusion is from a fable entitled The Donkey in Cuizlum in Three Disciplines by Liu Zongyuan of the Tang Dynasty.
故事出自唐代柳宗元的《三戒·黔之驴》，大意是说：
In ancient times, Guizhou (a province in China)had no donkeys.
以前，贵州没有驴子。
One day, a man full of fancy ideas shipped a donkey to the region.
有一天有个好事的人用船装了一头驴运到贵州。
However, he soon discovered the donkey was no use, so he took it to a mountain and left it there.
可马上他发现这头驴没什么用处，就把它放到一座山下。
A tiger saw the donkey and thought it was a mysterious beast.
一只老虎看见这只驴子，以为它是一种很神秘的野兽，
He hid himself carefully in the woods, and dared only to watch the donkey from a distance.
不敢靠近它，躲在树林里远远地看着这头驴，
One day, the donkey brayed.
有一天，它听见驴叫，
The tiger thought the donkey was going to bite him, but the donkey did nothing more.
以为驴要咬它，但它发现驴并没有采取什么行动。
The tiger soon got used to the noise, and moved closer.
渐渐地，老虎习惯了驴子的吼声，就慢慢地去接近驴.
At last，he decided to provoke the strange beast.
最后，它决定去招惹这头奇怪的野兽。
The donkey couldn't put up with this and gave the tiger a kick,
驴子很生气，给了它一脚，
but the kick didn't hurt very much.
但踢得并不重。
The tiger knew this donkey was weak.
老虎知道驴子没什么本事，
He sprang on the donkey and made a good meal of the donkey.
就立刻扑上去把驴子吃了。
Later, people use it to describe someone who is at his wit’s end.
后来，人们用这个成语來比喻仅有的一点伎俩也用完了。
。