英语问题：寻求经典表述——“早知今日，何必当初？”

It's too late to regret!

had known it earlier,never would done that.

If I'd known then what was going to happen, I wouldn't have done as I did.
早知今日，悔不当初。

regret一个词就可以把意思讲明了了。给外国人讲历史背景会很晕的。