The problem is that reality is complex, lots of special cases. Dates are a well known example, with lead days, leap seconds, time zones, DST, etc... So is local

The problem is that reality is complex, lots of special cases. Dates are a well known example, with lead days, leap seconds, time zones, DST, etc... So is localization. You may have the perfect code for your use case, with the right level of abstraction, until reality kicks in. For example, let's say you are writing a device driver, each device identifies itself with a unique identifiers, fine, until one day, you get different devices with the same id and you need to issue a special command to differentiate between them. And then, the next device receive commands in little endian order, even though all the other ones were big endian. And then another device sometimes silently fails to execute a command, you then need to a bit of time and check that it was actually taken into account and retry if it wasn't. Etc... You can't plan for all that, if you try, it will only make things worse. All that will invariably result in ugly code, it is not bad design, it is just that reality itself is ugly. If you try to start over, if you are really really good, you can reduce it to something nice until the next dose of reality. But more likely, you will make things even worse. Believe me, if you think you are good, try rewriting a legacy app that is used in production in a way that doesn't break production, I predict a humbling experience.