Well map here's the thing; no writer ever really knows if they're fooling themselves when they start out. It's very tough to judge your own work (I find it impossible even years later) because you're close in (or should be).
The best thing to do is to stop worrying about that and crack on.
Being a writer requires a certain level of arrogance. You have to assume that you have something to say, assume that people will want to hear it and assume that you can get what you have to say across. To strangers. On a macro level 
.
Getting a publisher is something to worry about down the line, when you've proved to yourself that you can write a full novel and that (for the most part) you enjoyed it.
Yes, it's hard to get published. Plenty of good writers never make it. That's because it's a business and a ruthless one at that. That said, there have never been so many debut novels published as now. The market wants more and more new books. Be optimistic wilst understanding that the being published or not isn't the definitive judgement on a writer's chops.
If you are published, will you make a living? Statistically, no you won't. The flip side of all those debut novels is crap advances and almost no effort on marketing. Publishers throw thousands of books out onto the market with the view that the cream will rise (personally I think this is a shite business model based on nothing true but there you go).
Writers must assume that they will need another source of income.
For balance, I'll admit that I do make a very good living from novels. I'm not JKR or even a household name (in the UK). But I have sold a book a year in very respectable numbers. I have sold lots of foreign rights of each book, audio book rights etc etc. I have also sold lots of options along the way (note to writers: keep option lengths short then when the production company can't raise the dosh, it reverts to you and you can sell it elsewhere).
So it can be done. Unfortuneatley there is almost nothing you the writer can do to influence such things. All you can do is write to the best of your ability, be prolific (I can't advise this strongly enough) and professional (stick to deadlines, don't strop over revisions).