For me it shows up in CI configuration (I always copy my old projects’ GHA files into new projects) and nix stuff (every project’s shell.nix is a copy/paste of the previous one, tweaked).

I feel like it’s a symptom of complex stuff you use too infrequently to fully internalize all of the details. You learn them when you need them, but when you don’t need anything new it’s so much easier to just copy some work you did in the past rather than trying to remember it all again. Make is in a similar boat: mostly you don’t work on it, you just use it, so you lose your specific knowledge between times that you’re actively working on it.