I've managed to write on nineteen of the past twenty days, for a grand total of 16,000 words, give or take a short story or two. There are certainly times I just want to give it up, but I manage to keep going. I think it helps to have experience writing in a not-necessarily-creative field. For example, journalists don't have the luxury of not writing; for them, writer's block equals not having a job anymore. Loss of income source is a powerful motivator.
For me, the non-creative writing comes in the form of technical writing. In one way, they are the bane of my existence: page after page after page of "Press this button, and this window opens. In order to add..." They represent boredom to the nth power. On the other hand, like with journalism, you can't just say "I'm not going to write today," unless you value your job very little. And, surprisingly, technical writing does help to develop your skills. The more you write, the better your spelling, stronger your grammar, and faster your typing. You focus less on the deceptive beauty of flowery language, and more on the nuts and bolts of getting your message across. At the same time, you develop various ways of saying a certain phrase to preserve interest in the most mundane situations.
I'm not suggesting all emerging authors go out and get jobs as technical writers, but it never hurts to consider writing styles outside of your main focus. Before I wrote the user manuals, I often found myself bogged down with painting the perfect picture with luscious verbs and tantalizing adjectives. "She swayed as the wind took her, and flicked about her mellifluous, auburn hair." I've learned now that whimsical turns of phrase do not a story make. It's much better to indulge in conciseness and clarity than thesauruses (thesauri?)