I have a folder of letters that were never sent. A few are angry and most are tender, and all of them were written in order to find out what I thought.
The act of addressing someone, even someone who will never read it, changes the sentences. They get clearer and kinder and a little braver. I think this is why the best essays so often read like letters: the writer has a person in mind.
If you are stuck on something you are writing, try beginning it Dear, and then cross that out when you are done.