The normal hatching sequence is that the chick internal pips, which means it punctures the air sac. Later, it external pips, then it eventually zips and finishes hatching. Also part of the hatching process the chick learns to breathe air instead of living in a liquid environment, dries up blood vessels it no longer needs and absorbs the blood, and absorbs the yolk. That is a lot of work. It may even take a break occasionally and just rest.
Some chicks do a lot of this preparatory work between internal pip and external pip. These usually zip pretty soon after external pip. Some wait until after external pip to do a lot of this. These worry us because it takes so long and we can see that they have pipped. Some even zip before they have totally finished everything.
It's possible a chick can't get past any one of these stages, but the majority work it out OK. If you try to help a chick to hatch before it has absorbed the yolk and dried up the blood vessels, you can kill it. I find the best thing to do is to do nothing. If you try to help, you are much more likely to do harm.