Quote Originally Posted by honeybeezercattalina
Why can they at times be hatched into chicks etc then?
Only in the very rare occasions as sweetpatata has mentioned.

The eggs have to be fertilised in order to become a baby chick. The ones you eat are not fertilised.

"If an egg has been fertilized, then the embryo inside has already divided several times but remains a group of unspecialized cells [at the time the egg is laid]. When the egg is incubated at about 37 to 38 °C, the embryonic cells differentiate to form a chick, which will hatch after 21 days. If the egg has not been fertilized, then the oocyte [or egg cell] within will never grow or divide, and the egg will never hatch. The eggs you buy at the supermarket are eggs that have never been fertilized.
chicken/egg link