Do you ever go back and read your own stories and still feel the same impact as the first time you wrote it?
Is it a thing about the writer to move yourself to laughter or tears? Is that when you know you’ve hit your audience?
I sent a particular story to a friend – I told her I cried while I wrote it. She said she cried while reading it and I called us both hormonal. (Sorry, friend!) But if that same passage keeps moving me to tears, and others as well, perhaps it isn’t just the hormones.
Now how do I keep that up?
Ransom Noble 
If it’s a repeatable effect and it impacts more than just you then it’s great writing.
The best is when I read something I totally forgot that I wrote and I go, “Wow, that author ought to be published! Wait… that’s MY work.”
I have that experience with stuff that I haven’t even written yet. I can be seeing the scenes in my head and become close to tears. However, I’m an emotional person and so it’s easier to get me crying.