I'm going to keep this short so as to give me an opportunity to work toward the goal this post is about, but the most important part of doing something you love is learning how to finish. Write the whole draft of a story. Learn to play the whole song. Paint the whole image. Dance the whole routine. And so on. It's easy for me, and everyone probably, to get excited about a new idea. To make big plans and promises and start out at a hundred miles per hour.
It's even easier, a day, a week, or just an hour later, to find us idling, not sure what we were so excited about in the first place.
This is the way to know you're an artist, I think. Absolutely anyone can start a project. It takes someone with passion to see it all the way through.