Vim: why doesn't ":normal! i" enter insert mode?

Question

In vim, if I execute the following from the command line

:normal! i

vim does not enter insert mode. Likewise the command

:normal! A

will move the cursor to the end of the line, but the cursor remains in insert mode.

Any ideas why this doesn't work? Failing that I would like to know an alternative way to enter insert mode from the body of a vimscript function (and have insert mode persist after the function returns of course).

Edit: Looks like :startinsert will fullfill the second part of the question, but I'm still wondering how I can do something like :normal! A or :normal! a and why those don't simply work as expected. Simulating "append" with arrow movements is a bad solution, because of things like empty lines and such.

Answer 1

The normal command considers ending in insert mode as an incomplete command and aborts. From help normal:

{commands} should be a complete command. If {commands} does not finish a command, the last one will be aborted as if <Esc> or <C-C> was typed. The display isn't updated while ":normal" is busy. This implies that an insert command must be completed (to start Insert mode, see :startinsert)

:startinsert might be the command you are looking for.

:normal A can be achieved by appending a bang (!) to startinsert, as suggested by Ingo Karkat. From help startinsert:

When the ! is included it works like "A", append to the line.