I've been writing software since the early 1980's and I remember being pushed to get it working and thinking "they'll rewrite this and fix it in the future, this is just to get it working now". It's been terrifying to realize over the years since then that no one ever revisited the code and it still has not been fixed in many cases. Some of that code was used to control trains, nuclear power plants, chemical factories, medical systems, and satellites. I suspect some of it has been replaced, and ultimately it was the responsibility of the people building those systems to make sure they worked correctly, but poorer countries often stole software and a lot of it was still seeing use long after the product was no longer even sold. The world is in some cases hanging on a thread of old software that no one understands any more and no one is supporting. Source code may not even exist.

I've worked in software QA also and abstraction is the bane of debugging, especially when you can't even see the code in the libraries you're using. Proprietary binary blobs in embedded systems are the worst.