It's nature. You can only control it as much as you can, the rest is nature on a crap shoot. The thing is - the more knowledgeable you are about what you are getting into, the higher the chance of success. Nature can hand you a curve-ball and you can make adjustments to still make a success out of it. You can see all the posts out here that, if it were left up to a novice without any help from the more experienced forum members on here, would surely lose the snake - like wrapped up/twisted umbilicus, mold, temp spikes, etc. etc.
My one and only breeding experience wasn't completely a success. I can look back and see where I went wrong (made cuts on the eggs that were too big, etc.). A more experienced breeder would have been able to hatch out all the eggs without a problem. At the same time, you kinda have to start somewhere to get that experience. So, yeah, STUDY STUDY STUDY! But, even after all the study, when you get an egg that hatches out a snake with extreme kinks, there isn't really much you can do about it.