Now it comes from the Latin words post scriptum, which means written after, so we use P. S as an afterthought, to add something to a message that you've forgotten to include.

它来自拉丁单词 post scriptum，意思是写在后面，所以我们使用 P.S. 表达的是事后的想法，把你忘记包括进去的信息给添加进去。