Writers Block
According to the Wikipedia article on Writer’s Block, Herman Melville stopped writing novels a few years after writing Moby Dick, due to writer’s block.
Who knows? Perhaps without that, the world might have seen a sequel named “Gilbert Gator”, in which an eccentric Captain Featherboot leads a shipful of befuddled mariners in the swampy bayous of Louisiana in pursuit of a toothless, albino alligator named Gilbert, believed by some to be the last of the dinosaurs.