I recently recalled a term from when I used to golf, which was about a thousand years ago. When a player was "grinding," he was fighting from behind in a tournament. Taking things shot by shot, digging in, and not quitting. In hockey, a "grinder" is a third or fourth line player. That player might not be the most skilled, but he works hard, going out and playing physical to help the team win.
I think in order to stick around for any length of time in the writing business (whether as an indie or traditional), you have to be a grinder.
Writing is often thankless. It can feel like you're yelling into the void and no one is listening. That you might never get where you want to go. That's when you have to grind.
Grind by hitting a daily/weekly word count goal.
Grind by submitting to publishers and markets, even when rejections pile up.
Grind by indie publishing work, even if it feels like you don't have an audience yet.
Grind by getting better at your craft and learning to become a better storyteller.
Grind by promoting your work (without being obnoxious about it, of course) and making genuine connections with people.
It's that tenacity and consistency that leads to more finished work, and hopefully meeting your writing goals. And remember to have fun. Grinding and working hard on your writing goals doesn't mean being miserable.