Comment by jenadine

Why is he wrong?

Here's an excerpt from the close(2) syscall description:

RETURN VALUE close() returns zero on success. On error, -1 is returned, and errno is set to indicate the error.

ERRORS EBADF fd isn't a valid open file descriptor.

       EINTR  The close() call was interrupted by a signal; see signal(7).

       EIO    An I/O error occurred.

       ENOSPC
       EDQUOT On NFS, these errors are not normally reported against the first write which exceeds the available storage space, but instead against a subsequent
              write(2), fsync(2), or close().

       See NOTES for a discussion of why close() should not be retried after an error.

It obviously can fail due to a multitude of reasons.