Why do chicks pip on the wrong end?

[newlyweds]

I just finished up a hatch of 21 Maran eggs, 14 successfully hatched. But as I was checking the unhatched eggs, I noticed that one had pipped through the shell at the wrong end, and then several more of the eggs, had pipped the membrane at the wrong end and drowned. So very sad.

I've had this happen with one egg before and was able to intervene and it hatched fine. But why did this happen to so many eggs? Any Ideas?

Thanks for your input?