I think it's true of anything in life. To succeed, you must have enthusiasm. Take a look at that definition. Absorbing or controlling possession of the mind. Ever feel that way about writing? I do.
Admittedly, there are many aspects of writing that just aren't that fun. (Typing. Submitting. Rejections, anyone?) But our enthusiasm for putting words on paper (or screen) can carry us through the tedious, difficult and downright heartbreaking parts. Creating characters, devising plots, finding skillful turns of phrase to describe it all. Yeah, it makes all the un-fun stuff totally worth it.
Your enthusiasm will shine through all your work. It will make your words sparkle. It will bring the stories to life.
How do you show your enthusiasm for writing?