Speedrunning Windows 95
Anecdote: back in the early 2000s, I regularly installed Windows XP on the machines of school friends and family members and got pretty fast at it. After a few months, I realized that I had memorized the original Windows XP "default" CD key (the one starting with FCKGW...) by accident. I haven't done an installation of XP in 15 years, yet you could wake me up in the middle of the night and I could tell you this damn key.