It was often the automated things that I completely forgot about. I have ADHD, so if it's not accessible in a reasonable way (where I don't have to always google specific commands to find basic info on my own machine), then it gets lost in the memory hole. I know that a service is running, but would forget what it is.

These days I have it pretty down-pat. Hardware is labeled, static IPs are set for "critical" VMs and LXCs (because I'm shit at DNS and still trying to get that down), and things are actually somewhat documented in an easy-to-find place.