Having written and published, for better or worse, Magic For Hire, I decided to write a sequel - another anthology. I then realized a certain demand for A) a novel, and B) a prequel. How did my protagonist end up the way he did?
So I set to work, and after 20,000 words or so broke my toes on the worst case of writer's block I've ever experienced. I'd gotten my protagonist into a predicament and couldn't decide on a way to get him out. I tried several, all of which were dismal failures. Today, at long last, a solution has suggested itself and the obstacle to my production melted in the heat from the keyboard.
My protagonist was in a bad way, through no fault of his own, but unless he could get out of his current predicament under his own power, he'd never develop and become the protagonist I'd write about later. My difficulty was that I was sending him help he didn't deserve. My solution is obvious; he'll overcome the problems that the author hands him without outside help, and continue merrily down the road to publication.
And that's how you defeat writer's block.