I am still in my learning curve phase of incubating and have tried various humidities, some with disastrous or partial disastrous results, and managed to save some that went on to be regular chickens. A dry egg is different from a defective, weak chick. If you know your temps and humidity has been off, or you had a bad temps spike, that is differrent from things humming along just about right and some don't hatch. Also, in the still air, there are areas of the incubator that are cooler than others, and that chick might just be a late hatcher. Sometimes I have ones that hatch two days after the others, because of still air, and those are usually the ones stuck to the shell that might make it. Ones that pip early and don't hatch, or peep and don't pip early, I don't try to help.