Board Thread:Spoilers!/@comment-2153169-20140925181009/@comment-24386552-20141111015639

The Mirror is merely a test of truth and self-control. And the strength of someone. Belle easily broke because all her worst fears and possibly some truths came to light in that episode where she saw the mirror. Something interesting, MM pointed out as that the SQ doesn't even need a mirror to destroy them, because everyone can easily just destroy themselves.