$ cat myfile.txt
cat: myfile.txt: No such file or directory
$ cat < myfile.txt
ksh93: myfile.txt: cannot open [No such file or directory]

$ echo one > one
$ echo two > two
$ cat one two # cat opens one, shows one, opens two, shows two
one
two
$ cat < one < two # sh opens one then opens two, cat shows stdin (two)
two
$ rm one two
$ echo one > one
$ cat one two # cat opens and shows one, fails to open two
one
cat: two: No such file or directory
$ cat < one < two # the shell opens one then opens two, fails and
                  # displays an error message, cat gets nothing on stdin
                  # so shows nothing
ksh93: two: cannot open [No such file or directory]