Some writers set out with a very clear goal: they want to write something that gets published. That might be a non-fiction book, an article, a novel, a short story...

Others have publication as a more distant idea: they primarily want to write, and they'll think about shaping that writing for public consumption at a later stage.

And, of course, a few writers don't want to be published at all. They simply enjoy writing for writing's sake – perhaps in a journal – and they have no intention of publishing.

None of these is "right" or "wrong". Writing for publication doesn't mean you're a grubby sell-out ... and writing for yourself doesn't mean you're being self-indulgent. 

I would suggest, though, that you're unlikely to get very far with your writing career unless you actually enjoy writing! If you only write because you want to see your finished book on the shelves, you might be better off hiring a ghostwriter and focusing on the things that you do enjoy (maybe you love marketing, for instance).

In some areas of writing, it makes sense to have a clear eye on publication right from the idea-stage: if you want to produce magazine articles, for instance, or if you're writing a non-fiction book to support your career as a speaker or coach. You'll want to develop ideas that work well for your target format and audience.

In other areas, though, too much focus on publication can inhibit your creativity. If you're a novelist or short story writer – and particular if you're a poet – then you may certainly want to angle towards ideas that seem like they could sell, but you definitely don't want to be second-guessing every character you develop and every plot twist you include. Write the story that you want to write first, and think later about whether, and how, you want to publish it.

Ultimately, if your pursuit of the end goal – publication – is making the process of actually writing feel like a miserable chore, take a big step back. Have a week off from writing. Spend some time playing around with writing just for the sake of it. Abandon projects that you took on for all the wrong reasons. It's great to write just for the joy of it, at least occasionally; you don't always have to have a productive end in mind!