Incubating an egg is not easy. You need to have the right temperature for the right amount of time, the right amount of humidity and a good, strong flashlight for 'candling' eggs, and even then, you never know how many of the eggs are going to hatch. It will, of course, depend on how many eggs have been fertilized. Discovering what's going on inside those shells can be a real challenge.
Hold the egg carefully between thumb and forefinger over a flashlight, candle or bare light bulb. Do this about three or four days after the start of incubation.
A fertilized egg will appear to have small spiderweb type veins inside the shell when it is 'candled'. An unfertilized egg will appear clear and should be removed immediately from the incubator.
Candle the eggs every third or fourth day to find out if the fertilized eggs are still viable. If they are, the spiderweb veining should have grown considerably larger and there should be a solid mass within the egg.
Candling will also reveal the eggs that are no longer viable, for whatever reason, by showing a dark mass that tends to slosh around in the shell when shaken gently.
Smell the eggs periodically. Viable eggs will smell okay but the rotting ones will naturally smell bad right through the shell. Dispose of any smelly eggs as these will eventually contaminate the rest of the eggs if allowed to remain.