There's one thing I want to tell you though. You don't have to sell a manuscript to feel like a successful author.
Writing is a business involving:
1. a learned set of narrative skills - grammar, spelling, plotting, characterization, viewpoint, scene and sequel, etc. If you don't know the full extent of narrative skills necessary, do yourself a favor and study so you can learn what you need to know.
2. the desire to tell stories - I think if you've got the desire to do something, that is an innate form of talent.
3. business sense - You need this to network, market well, get the professional assistance needed (that's an agent), take care of the money aspects of your career, learn how to promote you and your writing if that's in your game plan.
4. persistence - You must keep plugging away until success is achieved.
These characteristics are what all successful authors share in common. You notice that selling a manuscript isn't on the list. That's because selling a manuscript is something out of your control.
Do an inventory of your writing characteristics. How do you stack up? Room for improvement? If so, you know what to do. Get started on improving.
In today's world, you actually can control publishing and selling your book. That's what an independent publishing author does. If I can do it, anyone can!