为什么in fact 用在句首

in fact 一般放在句首,句中用逗号隔开,句末都行,不过我们见到的句首多些而已.
In fact would you like to join us?
事实上你愿意和我们坐一起么?

In fact, I'm like that as well.
其实,我也喜欢那样.

He was in fact hospitalized earlier this month.
本月初,他实际上是在住院.

In fact, he was tardy.
事实上,他是慢条斯里.

In fact no one knows.
事实上没人知道.

It already is a title in fact.

其实这已经是一个片头.
7.They hope, in fact, to kill two birds with one stone

实际上他们希望一石二鸟而已.