The one that always trips me up is that `ln` is “dumb” about how it handles the first argument.

If the first argument isn’t an absolute path, it must be relative to the second argument, and not to pwd.

    ln ./foo ./bar/baz

./bar/baz will be a symlink whose literal contents are `./foo` so it will look for foo in the same directory (bar), rather than in bar’s parent directory.

This is totally backwards from how other utilities behave. Which is completely understandable if you know what it’s doing under the hood. But it is counterintuitive and surprising.