Additionally,

    $ f=-x
    $ cat "$f"
    cat: invalid option -- 'x'

    $ cat -- "$f"
    cat: -x: No such file or directory
    # ^-- correct, but:

    $ f=-
    $ cat -- "$f"
    reading stdin...
    reading stdin...
    ^C

    $ f=./-
    $ cat -- "$f"
    cat: ./-: No such file or directory

...better to glob with ./* than *