Not all of the fish that come in the common eggs breed well. If you keep track of what you breed and what dies, you can soon figure out which ones are safest to breed. I find there are three body types and three fin types that are always safe to cross.
Lots of breeding is good if you use it to figure out which ones are produing good fish. You only need produce one good baby, if you know who the parents are, because then you can breed another one and start breeding those two and build up a breeding stock. It's a slow process at first, but ever so much fun when it works!