"The Mythical Man-Month" by Brooks says in a complex system such as the old IBM 360 operating system, there is an irreducible number of errors. The problem is that in fixing errors, further errors are created.
Recently I reinstalled the Windows Vista operating system. After re-installation, Microsoft downloaded 102 updates and now there have been several days of additional system updates and service packs. This from the world's most famous, most experienced software company! Imagine the errors in the human genome or in the annals of American law. Clearly, the genetic process of creating a baby can produce all sorts of errors.
Many people are highly focused on avoiding errors and that is a good thing. But in my opinion, it is better to expect some downright mistakes from ourselves in all our activities, from eating and breathing and walking to writing or piloting a plane. The book by Tom Wolfe, The Right Stuff, tells of the battle between pilots with terrific courage, reflexes and physical skills and the engineers who grasped the limits of humans and wanted to guide space rockets with foolproof systems they were confident they could build. As is often the case with a pitched battle, both sides were right and still are. Humans do make errors, competent ones much less so, but they still make them. That means that planners and builders and assemblers also make them. Even when we create a system that works exactly as we intended, we sometimes find that the situation is a bit different from what we thought it was. Then, the system or machine or arrangement or deal or treaty or patent doesn't fit reality the way we hoped.
Despite the awe-inspiring abilities and complexity of the human brain, Johns Hopkins neuroscientist David Linden emphasizes in The Accidental Brain that the brain is a hodge-podge of evolutionary developments and drifts that are not super-engineered or totally rational. Melvin Konner in The Tangled Wing impresses the reader with the complex process of the development of a brain in the fetus and the precarious trip that some neurons have to complete across a wide space to make the unborn baby's brain functional.
