Because your keyboard is stuck on permanent caps lock and you cannot remember the alternative to ':wq' which you cannot enter due to the perma-caps input device that requires a reboot to become a keyboard again.
If you use Synergy then this happens and a reboot can be easier if you are stuck.
In theory you really could forget 'ZZ', I nearly forgot '=aB' for some reason recently, this '=aB' to indent is only really known in muscle memory and the actual '=aB' text is entered and gone quickly from the bottom of the screen, so never seen, merely memorised as muscle memory, not a written or vebalised thing.
[1] https://twitter.com/iamdevloper/status/435555976687923200?la...