原来如此。一经你解释我就明白了。

[误] So it is. I understand soon after your explanation.

[正] So that's how it is. I understand soon after your explanation.

注：So it is 的意思是“的确如此”，它是用来表示对对方观点的赞同的。例如：

A: It is a fine day today!
B: So it is.

而在表达恍然大悟时，英文要用 So that's how it is 或 So that explains it, 或更简单地道的说法

Oh, I see.