Jody is correct about what she said, however, I have had a few instances with one particular hen's chicks where, although the humidity was 35-50% during incubation, they grew too large for the egg to pip the shell. At least, that's what it seemed to be when I assisted the humongous, perfectly formed, but just deceased chick out of there. It did seem to be crammed into the shell so it couldn't position itself. Perhaps it just for some other reason, was in a bad position to pip, so I could be incorrect and making the wrong assumption. So much we don't know unless we can see into that egg. Boy, sometimes, I really wish I could!