The scheme has a snowball's chance in hell of being accepted.

这个计划根本就没有希望被采纳。

But it hasn't got a snowball's chance in Hell. Believe me, I know.

但是相信我，这机会还没有烈焰地狱里的雪球大。

Let's say you applied for a promotion at work. But so did your boss's daughter. You do not have a snowball's chance in hell.

比如说你申请晋职，但是你老板的女儿也申请了，你就毫无机会。