“They keep trying, don't they?" he said, thoughtfully. "The plovers, and that little bird with the feather, all of them; they're still working so hard. All those hours and hours building their nests and finding those white feathers and laying their eggs."

"Birds always keep trying," said Castiel, nodding. "Always. A wild bird never gives up. Same with the wolves. They never give up. I've never yet seen a wild bird, or a wolf, that felt sorry for itself. Till the end, they just keep trying.”