I remember leaving off the initial "I" for insert-mode a few times when writing long TECO edits. Hitting the double escape and realizing in horror that the edit

I remember leaving off the initial "I" for insert-mode a few times when writing long TECO edits. Hitting the double escape and realizing in horror that the editor was parsing my assembly language program as editor commands wasn't fun. That got fixed eventually iirc by keeping your text input in a buffer. By the way, TECO was a CHARACTER editor, not a line editor!