他生病了，所以没有来。

He is ill so he did not come.

我们以前见过，所以还相识。

We have met before, so we know each other.

他当过教师，所以教学经验他是有的。

He has been a teacher, so he has teaching experience.

我急于要赶回家，所以没有能到你那儿去。

I was hurrying home, so I could not get to your house.

我本不想去，所以就没有去。

I didn't want to go, so I didn't go.

先进分子之所以先进，是因为...。

The reason that advanced elements are advanced is that .

他之所以拒绝，是因为他不同意大家的意见。

The reason he refused is that he does not agree with everyone's opinion.

我曾和他同学六年，这就是我所以对他比较熟悉的原因。

I was his classmate for six years, and this is why I know him quite well.

所以呀，要不然我怎么这样说呢。

That's just it. Otherwise, why would I say this?

所以嘛，早就该这样。

That's just it - it should have been like this long ago.