置之死地而后生

西汉时期，刘邦派大将韩信和张耳率军攻打赵国，赵王刘歇和大将陈余率20万大军在井陉口迎战。陈余不听谋士李左车的建议，与韩信硬拼，韩信故意置之死地而后生在河边列阵，士兵们背水一战，越战越勇，然后派兵轻取赵军大营，杀死陈余，活捉刘歇。

It originally meant that when the army was placed in a situation where it could not retreat and only died in battle, the soldiers would advance bravely and kill the enemy to win. The latter metaphor is that if you cut off the retreat in advance, you can make up your mind and achieve success.