Failure to thrive just happens sometimes. I have one right now, came from a shipped egg, and it's at least partially blind and refuses to even try to eat, even when we put a small piece of hardboiled egg in its mouth, it swallows, but doesn't act like there is any interest in living. You can force feed it and put water in its mouth with an eyedropper, but if it won't start on its own, it will die within four or five days, usually. It's just one of those sad things about raising chicks.