Writing and publishing an article and a newsletter are very different experiences.
In the first case, you put something in the world to be seen. Like to throw a bottle with a message inside to the sea. Or like hanging a cartel on a school cork-board.
In some way, the object of your creation has your name on it but it’s not yours after you publish it — it’s part of the world. Readers are abstract.
In the second case, you aren’t putting your text on the world but directly sending it to some people.
The object of your creation isn’t part of the world in general but part of someone’s inbox. Your letter is invading someone’s space. Readers are concrete and have names.
I always feel a little nervous before publishing an article or blog post, but the stress is stronger when I send a newsletter.