Having seen machines that have hundreds of Vim sessions opened because “system integrators” didn’t know how to exit Vim, it should be the very first thing taught
Luckily vim finally got a bit better with that: on a Ctrl-C newer versions now show instructions for quitting.
I remember my first vi sessions (typically via something like `crontab -e` where it wasn't clear to me it picked my "default" editor ... thus didn't know where to read up on it ...) some long time ago, where i knew `kill` before the right command ...