There's an initialism for it, used by the people who know about the feature to describe the people who didn't: RTFM.
If I read the manual for everything I've ever used, I'm not sure I'd have time to actually accomplish anything in the end.
Sure, let me spend a day reading through the lists of keyboard/mouse shortcuts for every piece of software I use just to see if there's anything useful in there? No thanks...
Good UX would pop up a balloon informing me of the feature after the first time I held down my left-arrow key for more than, say, keypresses.
Of course, you might as well disregard the manual and discover things on your own as you need them. Nevertheless, it helps to go at this with a mindset of "this feature surely already exists" lest you're compelled to develop a worse version of the feature yourself.