Sometimes chicks don't "zip" to get out of the egg

A lot of people are going to say this is false, but in my experience and I have hatched hundreds of baby chicks, occasionally there will be a couple of chicks that don't zip the egg so they don't break a straight line all the way around the egg and open it up like a cap, I've had several just break a hole in the egg and try to squeeze out some of them do get out some of them stick their head out get stuck can't get their head back in and need help.

Here is a Chick that is currently trying to hatch, I've not assisted this chick and don't think I'm going to need to because it has been actively chipping off pieces of egg, it's just chipping it off in a circle for some reason which as long as it comes out healthy I don't care how it chooses to hatch, I just think this is pretty cool that they don't always follow the book