既来之，则安之的英文：
in for an inch, in for a mile

参考例句：

Let's cross the Bridge when we come to it
既来之,则安之

Now (that) you are here you'd better stay.
你既然来了，(最好)就呆着(或住下)吧。(既来之，则安之。)

inch是什么意思：
n. 英寸；身高；少许
v. 使缓慢地移动，渐进

not budge an inch
一动也不动|毫不改变主意

My soul was coated inches and inches thick with perjury
我的灵魂深深地陷入了伪证罪之中。

Men are not to be measured in inches
人不可以寸量/人不可貌相,海水不可斗量

Men are not to be measured in inches.
人不能以高矮来衡量。

An inch in a miss is as good as an ell
错无分大小,有错皆不好

mile是什么意思：
n. 英里；相当大的距离；相当大

Miles and miles of white interspersed with blue.
连续数英里的白色用蓝色点缀着。

Cheerful company shortens the miles
旅有好旅伴,不觉行程远

Hello, Mrs Miles.
您好，迈尔斯夫人。

The forests stretch for hundreds of miles.
森林绵延数百里。

Miles upon miles to the east and southeast the desert unrolled itself
荒野绵延万里的向东面和东南面铺展开去。