Not everyone is a ebook lottery winner. Not everyone is going to be the next member of the Million Kindle club, but that is not a reason to stop writing.
The passionate writer, writes for the sake of the art, and the overwhelming desire in their soul to share the story with the world.
There's a theory out there in the universe: 10% of all people are not going to like you; as a person, but you have to focus on the 90% who do. If you put all your effort into trying to woo the 10%, eventually you will begin to lose the 90%. I think this is true of writers too.
Not every reader, or reviewer, is going to like what you write. There are many reasons for their opinions, but you have to remember, the value or likeability of the story is subjective, and again, opinion based.
Writing constantly improves the skill. I know this first hand. I'm not perfect, I make mistakes. We all do. I still write. I still try.
Don't give up your dream due to mistakes and slow progress. At least you are trying. When you try, you are way ahead of everyone else who doesn't.