what is done is done 可以译为“木已成舟”,它还有一个类似的习语表达方式 you've made your bed,还可以译为“做了决定”寓意:

1、to make a decision and to accept the consequences of those decisions
做出决定并接受这些决定的后果

2、to have done something in the past which is either good or bad and to bear the ramifications of it
过去做过好事或坏事,并承受其后果

3、to accept and bear the repugnant results of the deeds committed by oneself
接受并承担自己所做的事情的恶果

它还有一种更完整的表达方式:you've made your bed , you'll have to lie in it / now lie in it,译为“了决定,你就得承受这个结果;自作自受”等

例如:

1、Don't come back when it is all over and you have nowhere to go. Once you've made your bed , you'll have to lie in it.
当一切都结束了,你无处可去时,不要回来。一旦做了决定,你就得承受这个结果。

解析:nowhere 在这里相当于 no place.

2、You can't go back to them when this does not work out. I'm warning you because you've made your bed and you'll have to lie in it.
当这个行不通的时候,你不能再回去找他们了。我警告你,因为做了决定,你就得承受这个结果。

3、My mother always told me to make the right choices because once you make your bed, you have to lie in it.
我妈妈总是告诉我要做出正确的选择,因为一旦做了决定,你就得承受这个结果。

4、The mistakes you made are all yours. You've made your bed and now lie in it.
你犯的错误都是你的。你做了决定,你就得承受这个结果。

解析:此处省略了关系代词 that 或 which,因为它们在定语从句中充当宾语的成分。