For me it’s my Windows 98 CD key (25 digits alphanumeric). I had to wipe and reinstall so many times that it saved a lot of trouble to commit it to memory. And

For me it’s my Windows 98 CD key (25 digits alphanumeric). I had to wipe and reinstall so many times that it saved a lot of trouble to commit it to memory. And now here I am 20 years later...