`tar -xfj foo.tar.bz2` would extract the file `foo.tar.bz2` from inside the archive `j`. IOW, it's providing `j` as the argument to the option `-f` that's used

`tar -xfj foo.tar.bz2` would extract the file `foo.tar.bz2` from inside the archive `j`. IOW, it's providing `j` as the argument to the option `-f` that's used to specify the archive file. It should rather be `-xjf`. Also, case matters, `-J` is for .xz files, not .bz2. `tar` has a pretty simple calling syntax, probably simpler than most utilities. I encourage people to use the manpages instead of cute but wrong or misleading mnemonics.