As I've mentioned before, the first systems on which I used Emacs had keyboard support that was spotty-to-nonexistent for anything but the most common keystrokes.
Consequently, I learned to use ESC for a lot of stuff where you'd use
Meta. For most of those things I've retrained myself, but until I was
actually reading the GNU Emacs Manual, I didn't know that you didn't
have to hit ESC to do a numerical argument.
So where I've often done ESC 5, say, to do a numeric argument to a
function, I've now learned that I can simply do M-5, which is more
like a single keystroke.
I do expect it'll take a bit to train myself out of my existing habit, but I'm hopeful.