Whoever come up with the idea of "God", a grand genius master architect, clearly had no understanding of how unbelievably shitty the engineering of living organisms is. I really cannot emphasize enough how poorly designed our bodies are. A physical manifestation of uncommented, heavily obfuscated, spaghetti code that's only viewable and editable in binary. And every "program" (human) is different and unique.

Yes, living things are amazing, but any designer approaching even basic levels competence factors in repairability and serviceability.

So all that is to say: It's crazy complex and any single thing is liable to have myriad first order, second order, third order...30th order negative effects.