"Bite the bullet," or doing something unpleasant, comes from when soldiers would bite a bullet when they were being operated on without anesthetic.
“咬子彈”（bite the bullet），即做令人不愉快的事。這一習語來源于過去士兵們做手術不打麻藥，只能咬子彈忍痛。

There is some debate over whether or not this is true. The phrase has been in use since 1796 and has always meant to have a "stiff upper lip" before doing something you don't want to do.
關于這一來源是不是真的還存在爭議。這一短語從1796年就開始使用了，總是用來指在做不愿做的事情時咬緊牙關（have a stiff upper lip）。

It may have come from a belief that people can derive courage from biting a bullet, according to researchers.
研究者稱，這也許來自于一種信仰，認為人們能從咬子彈中獲得勇氣。