-is, on at least one level, learning about yourself. Not in a "voyage of self discovery" way, but in learning how you work, and how that's different from how you'd like to think you work.
I've been futzing around with the second half of the opening to Hero's Army (the sequel to The Wrong Sword) for literally months. I never got past that point. Just kept returning and returning, fine-tuning prose that didn't need it, inserting scenes that weren't necessary. I couldn't get past it.
I finally figured it out.
1. There was no reason for the protagonist to stick around, but I had pages and pages of him doing just that.
2. Unlike other, smarter writers, I couldn't just stick a pin in the damned thing and come back to it.
Got to get better about that.