I sometimes wonder if writing is just:

A form of self-therapy.

Or:

The expression of a desire to be admired/loved/respected/whatever; thereby abdicating responsibility for oneself and putting it in the hands of others.

Or:

Motivated by a (naïve) desire to change the world.

Or:

Driven by a hankering to find a way of making money and have a comfortable lifestyle by not having to do the dull and dreary job that one does. And have one’s ego stroked at the same time.

Or:

Prompted by the assumption that a ‘significant’ number of people will/should be interested in what one has to say.

But:

Some seem to write simply because they ‘must’.

A friend of mine (unpublished, apart from a short volume of poetry) is a vastly superior writer to me; genuinely, supremely talented. I asked her; if she was the last person left on earth, would she still write?

She said she would.

“I don’t write for other people, I do it for me.

“If I was on a desert island, and I didn’t have pen or paper, I’d write in the sand. (The tide would wash it away – my words.) And I’d write something else again the next day.”

I believed her.

I write because I really can't stand being bored. And I also, probably niaively, think I'm achieving something JD

I think writing can sometimes, for me anyway, merely be a form of control.

You can't control the real world so you create your own.

If something happens in the real world that I haven't liked I'll replay it in my head with a better ending; a kind of mental script. A kind of, "if only I'd said..... " response.

Arguments get replayed with a new script entirely to my liking.

With writing if you don't like the world you have created you can rewrite it.

First you wonder if you can write. Tell stories.

Then you wonder what stories to tell.

Then you wonder what people will think.

Then you start to seek advice from "readers".

Then you are back at step 1. "...the likes of NickP can rant on if they like"

I occasionally rant on at http://amonsterinthemirror.blogspot.com/

I went through writer's block for a few years. It was a mixed bag of emotional crap and physical pain that caused it, but the answer to it was remembering why I wanted to write anything in the first place.

I just wanted to explain myself. I thought, for a long time I was trying to explain how I thought, why I thought, and what I thought, to other people. Now, I know it was far more internal than that. It's explaining myself to myself. And then, if someone else even halfway understands it, then I can consider myself at least partially sane. When your work speaks for itself, don't interrupt.
Henry J. Kaiser (1882 - 1967)