Why does Mother cat abandon a kitten?

In some cases the mother cat knows the kitten is dying, such as the runt of the litter, and she abandons it to give her other kittens a better chance of survival. Another reason a mother cat will abandon the kitten is caused by the mother being far too young to have a litter, and therefore abandons a kitten (or all of them) because she is overwhelmed or not know what to do.