Unhappiness is linked to wanting. It's a feeling of entitlement you can't shake easily.
You get caught up with what you're doing and sometimes you can get to where you think you deserve.
I find that it's best to not pour all your hopes and wishes into a single project, because it may not work out.
Like has been said, write for yourself foremost. It's hard to do that when you're serially releasing a story just as soon as you write them, because doing that means your focus is on the reader and not yourself.
Writing a story entirely before releasing can help, nya! But don't think it's just for the sake of making the piece as polished as possible, but just don't get stressed over it. It's more about giving yourself space until you're ready to commit.
And when you do, be pleasantly surprised if it's a hit!
It's a tasty cookie you didn't know you had in your sweets stash!