When I've tried to hatch them in the incubator they'll pip & stop. By the time you give up waiting for them to do it naturally they're either dead or you'll pull them out & one of two things will happen. You'll peel the membrane & it'll bleed more than you thought & they'll die or you peel until you get blood, stop, repeat the next day, and by the time you can get them out of the shell they're basically froze in an awkward position & flop around and never improve. There are those who seem to fully develop but just won't pip, too. I've had great success hatching eggs in an incubator that had been started by a duck ... such as when I rescue a nest for whatever reason, but I've never had much luck hatching eggs I started in the incubator. Some will report having fantastic luck and while I do believe that some can be successful with it, I'm extremely skeptical of a lot who report such outstanding hatches without any problems.
It was really interesting at one point I'd rescued a nest that had been under water all night after a severe thunder/hail storm. My philosophy is that eggs aren't dead until they're warm and dead (much like human medicine!) so I always throw them in an incubator and wait until they've warmed up before I candle and out of 9 eggs, 8 were fertile & 7 hatched. I was impressed! Just thought that was really neat!
