When writing is a hobby, it's fun. It's fueled by passion and inspiration and excitement. When it's a job, it's fueled by the same thing, but instead of being able to put aside a current WIP in favor of a new idea or taking an impromptu two week break or just deciding to set a WIP aside, you can't. Because it's your job.
One of the biggest fears I have is that when I start the second book for the three trilogies I'm writing, I'll lose that spark that made me love it in the first place. Kind of like getting over the honeymoon phase in a romantic relationship.
Even as I write this third book in my third trilogy, sometimes I just want to stop. Not because I don't think it'll be a good book (how many YA pirate novels are there?) but because I don't want to get up early to write. Because I'd rather be reading. Or sleeping. Or watching television. Or going to a movie. Or Tumblr. Or doing anything except writing.
It can get tedious to write every. Single. Day.
As a Sagittarius, I get over routine really fast. But it's that routine that triggers my creativity. It's a muscle you have to work constantly so muscle memory builds and when I sit down, ready to write, the ideas come because I've built up that muscle memory over time.
When I write, I'm excited but there are times when it feels like work. But when I type up my manuscript, I reread my words and I realize they're good. I might not realize it when I write, but when I read it, it reminds me that this is what I was born to do. And I'll continue to do it, especially when it feels like work.