In about 1990 I got tasked with building an installation and configuration system for the hardware and software package my company built. It was an Ethernet car

In about 1990 I got tasked with building an installation and configuration system for the hardware and software package my company built. It was an Ethernet card and a TCP/IP suite being added to the PCs of the era (that had an AT/ISA bus where you had to find a free address block, then jumper the card to have the correct address, lotsa fun.) I wrote the first system targeted at AT&Ts Unix for the 386. After it was completely done, I was assigned to do the same for Xenix. After that was completely done, I got assigned to do SCO (Santa Cruz Operation) Unix. After that, Interactive Systems (ISC). Each system had its own architecture for installation and configuration. I didn't know in advance anything about the different systems, nor any knowledge that the other systems were on the horizon. As I was writing the second system, I was refactoring like mad to avoid duplicating code, and feeling very proud due to previously learning the horrors of duplicate code. I can't remember details, but among other things files had to be placed in a specific directory hierarchy for each system, and various files had to perform certain (different) functions on each system. When I turned to the third and fourth target systems, the refactoring just became weirder and more complicated, but I was determined to avoid duplication. Historically it turned out we never revised these releases. With 20-20 hindsight, it's a case where the refactoring was completely pointless, and code duplicated 4 times would have been way faster to create, and easier to maintain if we had made new releases. I think part of Sandi's point is that YAGNI applies as well ... a higher level abstraction may accommodate changes that never arrive, or the changes may be so large that NO abstraction will cover it. On the opposite end of the spectrum, in 1980 (yeah, I'm really old) as a summer-hire, I'd written in HP-Basic this very funky single-purpose very primitive data base system. When I returned 9 months later after graduating, two full time guys had made small changes to the system, but one guy had made a breaking change, the other guy got pissed off and duplicated _the entire program_ (a single file, to be sure) and made one small change. Thereafter I had to maintain two versions of the thing. Gaaack. It was the ultimate lesson in "don't duplicate code". (It was also in the days before we had a version control system or diff, so backing out and correcting the change wasn't practical.) Mel, where are you now?