A thing that nobody ever seems to mention which unsettles me far more than learning key commands or modal behaviour in my brief tryouts with Vim is how its cursor visually highlights a current character rather than a point between characters like every other editor I've ever used.

Say I have a line as follows:

  abcdef

In other editors:

  to delete "abc" from the left:
   put the cursor on the a
   C-d C-d C-d

  to delete "abc" from the right:
   put the cursor on the character after the c (the d)
   C-h C-h C-h

  to delete "def" from the left:
   put the cursor on the d
   C-d C-d C-d

  to delete "def" from the right:
   put the cursor on the character after the f (the EOL)
   C-h C-h C-h

Symmetrical and consistent, to my mind.

In Vim:

  to delete "abc" from the left:
   put the cursor before the a
   xxx

 to delete "abc" from the right:
   put the cursor on the character after the c (the d)
   XXX

 to delete "def" from the left:
   put the cursor on the d
   xxx

 to delete "def" from the right:
   put the cursor on the f
   xxx

The last case there is exceptional. It's a small thing, but not being able to put the cursor on a real or virtual 'end-of-line' character in Vim makes me feel constricted.

I think that the between chars cursor model is simpler because you then have two choices: act on the preceding chars (thus, delete with C-h or <Backspace>) or act on the succeeding chars (thus, delete with C-d or <Delete>). By contrast Vim is more complicated because from the current character you have three choices: act on the preceding chars (thus, delete with X), act on the current char (thus, delete with x), and the principle of 'completeness' suggests a third: act on the succeeding chars - which AFAIK is not available in Vim and so it feels lop-sided to me.

Ironically I think that it's my 'programmer head' which makes the between chars model appeal to me more, as I think of the file as a bunch of bytes (well, maybe multibyte characters) and the text editor as a glorified hex editor, and I just want to choose a position and insert or delete chars regardless of whether they're alphanumeric, LFs, or whatever. Whereas Vim's model of manipulating words, lines and sentences suggests to me a fit with people writing in human languages. Why, non-geeks should love Vim, perhaps except for all the key commands to learn; one imagines an alternate universe where the common keyboard evolved with two Return keys instead of one, labelled "Open new line above" and "Open new line below", and other Vim-inspired niceties - and I wonder whether your archetypal 'grandmother' might find it easier to write letters on the computer in that world than her current futzing about in Microsoft Word.