Yeah, I'm not sure I'd even call it a command - but it is pretty fundamental to vi usage, unless you're using some alternative like ^C or the "remap typing 'jk' to Esc" trick. When you're saying you've never used the Esc key, you mean you only use the Esc key to take you out of insert mode, I guess?

Yes. I do use ESC that to exit insert mode. Sorry for any confusion.

I was expecting commands to be anything you did after the typing in colon.