Why Don't all Bird Eggs Hatch

Infertility, poor nutrition, hen doesn't sit on eggs (cold eggs), bacterial infections, etc. It is not always easy to determine why some eggs just don't hatch. In my experience, usually one or two eggs simply don't hatch. It's usually the last eggs laid. Consider the obvious: a hen lays six eggs. The first few are going to get the "best stuff". This might sound simplistic, but in nature, the smallest baby often does not thrive; hence, the term "runt." I have had a few runts who did quite well in the long run; they simply required a longer weaning time and more care. Some of my best and sweetest babies have been the runt of the clutch. Nature knows best. Not all eggs are meant to hatch. Obviously if none of your eggs are ever hatching, you should be concerned. But I would not be overly concerned about one or two not hatching in a clutch; I think many people overreact to this. Believe me, in nature all the eggs do not hatch every time.