it's now or never
机不可失，失不再来
释义：
If you say 'It's now or never', you mean that something must be done immediately, because if it is not done immediately there will not be another chance to do it. 机不可失，失不再来
例句：
It's now or never, so make up your mind.
Much as I hate to go, it's now or never.
