螳臂当车 – táng bì dāng chē – “a mantis trying to stop a carriage”
As this story goes, there was a very strong mantis, who could destroy all other mantises in fights. Of course, this mantis got a little cocky as a result of this. One day, a coach was driving by on his horse carriage. The over-confident mantis decided to raise his arms in an attempt to stop the rolling carriage. The driver ignored the stupid mantis, and kept driving straight. Of course, the mantis was run over and killed as a result of his foolishness.
Meaning: Overstating one’s abilities and trying to do what is beyond one’s power.
Usage: Used to describe an over-confident, self-important person.

"When Duke Chuang of Ts'i (B. C. 794-731) once went ahunting, there was a mantis raising its feet and seizing the wheel of his chariot. He questioned his charioteer as to this insect who said in reply : 'This is a mantis ; it is an insect who knows how to advance, but will never know how
to retreat ; without measuring its strength, it easily offers resistance.' The Duke answered: 'Truly, if it were a man, it would be the champion-hero of the empire.' Then he turned his chariot to dodge it, and this act won him all heroes to go over to his side."
As time passed, the meaning of the phrase changed to its opposite. Now it means that someone overrates oneself and try to hold back an overwhelmingly superior force.