Oddly, I find that "picking at it" without any metric of success/failure usually reveals that I actually can do it, it's just that I'm terrified of failing. I've been trying to redefine a lot of my success/fail metrics so that such dabbling is considered a success, and failure is instead a lack of any progress/effort, and finding it's helped my productivity in a lot of areas.

Now that I'd rather write badly than not at all, I do a lot more good writing :)