The chips are stacked so high against breeders its a wonder that anyone does it.
You need to start with a whole bunch of luck–that the mare gets in foal, that the pregnancy is uneventful and the foaling routine, that there are no paddock accidents, sickness or other calamities that strike down either the baby or the mare or both.
Then the baby needs to have some quality–not too small or crooked or plain.
Then the stallion you perhaps took a flyer on needs to still have some commercial presence.
Then your luck needs to hold as the baby matures and again no paddock accident, sickness or other issues. (I suspect the uninitiated might be amazed at the X Rays of babies just coming out of a field where they were allowed to roughhouse and just be horses. A friend of mine getting bad news about his yearlings after routine pre sales prep X Rays exclaimed “Did they drop them from a helicopter?”)
Occasionally routine pre sales scans give you the worst of all news “unraceable”. These could include OCDs, cracks where you didn’t realize they existed and/or breathing issues. Sometimes this does not doom the horse–every one has a story of a horse pronounced by vets to be unraceable who turned into quite the racehorse. Chances are good they existed before the widespread use of X Rays when people just took it on faith they could buy, break and race the yearling in front of them.
The point is that stallion selection is one of the few things breeders can control. If you get a baby, the baby will be by X because you signed a contract for X. That’s why, I think, breeders flock to the same handful of stallions particularly if they are trying to be commercial. It’s a way to deal with rest of risk which can be overwhelming if you start to think about it.