"背水一战" (bèi shuǐ yī zhàn) is a Chinese idiom that translates to "to fight with one's back against the water," which means to be in a desperate situation with no way out, and thus must fight bravely or die trying. It comes from an ancient Chinese battle strategy where soldiers were placed in a position with no retreat, forcing them to fight more courageously. This idiom is often used to describe a situation where someone has to face a difficult challenge or task with all their effort and determination, as there is no other choice but to succeed.