Jeff Goins blogs about The Wrong Reasons to Write. I only qoute the lists, Jeff expands more on them in his post.

The wrong reasons to write
You want to be heard.
You want to be famous, to make a name for yourself.
You want to impress people with big words and sound smart.
You want to make a ton of money.

The right reasons to write
You have something important to say.
You want to make others feel understood, like they’re not alone.
You want to make a difference with your words.
You want to teach the world something it wouldn’t otherwise know.

I struggle with my own, often non-existing, writing. To me Jeff’s right reasons to write makes sense when it comes to writing with the purpose to share it with others. Having something to say and to make a difference, to have an impact, are terrific reasons to write. I’m still mostly writing for myself, to get into the habit of writing.