Please write:
echo "12345789"
and insert the missing number without deleting the already existing numbers in a vanilla (non-emacs, non-vim) terminal. In nearly every other editable text field people know well in their lived (including the one you typed in for this comment) you can move your cursor to the middle of a sentence and insert text with a mouse click or the left/right arrow key.And before someone suggest some option to enable this: my comment was about changing the defaults.
Some terminals also support mouse navigation, so keep an eye out for that as well.
I'm sorry that you've been dealing with this frustration for so long and under the impression that it was just supposed to be that way and not fixable. The good news is that it's NOT supposed to be that frustrating and you CAN fix it
Edit: you edited your comment somewhere between my first seeing it and my reply posting. I haven't had to modify the default settings on my terminal to fix things like this in about 20 years. I've changed them to tweak various preferences like scrollback, cursor shape/size, etc. But arrow navigation has worked out of the box for me for so long that I literally can't remember when I last had to fix it. I don't know why our experiences have been so different, but I'm sorry that a tool that has been so useful for me has been so frustrating for you.
Old enough terminal or old enough host, sure, there can be some fighting involved. Of course, working in those conditions, sometimes backspace doesn't work either and you have to hit ctrl-H like an animal.
But I haven't had issues with that lately.
If arrow keys not working for you, install a new distro.