补充:The truth is也可以不用作插入语。如:
The plain truth is that he doesn't like you. 说白了,他不喜欢你.
在“The truth is + 逗号”后面应该是一个完整的句子。又如:
The truth is, I was slightly predisposed against him. (外语教学与研究出版社2006年10月第1版 《英语搭配大辞典》p.1804)
下面的句子中的逗号都应该去掉:
My birthday is, on May 16.
Some of the students are, from the south.
All the money is, for you to buy the house.