My main problem is that I don't realize which mode I am in each time I use vim.
Sometimes I forget to <ESC>
into normal mode, hence pressing vim commands in
insert mode. I have to waste time deleting those characters, but that's not the
worst.
The worst is when I don't realize I am in command mode, and I do several characters of typing. Then I realize, gosh! I made a mess to my notes. I don't know what have I changed, and that's my nightmare. To undo them back to the correct state is hard because I don't know what the correct state is.