Kabbalah

Nothing is by chance: every single event or experience in a person's life is predetermined and purposeful. So if a person chances to witness the degradation of his fellow, he must realize that he, too, suffers from the same lack in one form or another. Otherwise, why would Divine Providence have caused him to see his fellow's failing? Obviously, to open his eyes to something he must correct in himself. So even if one is your enemy, and justifiably so; even if his moral and spiritual downfall is one of his own making - it could have happened without your having been made aware of it. That you have witnessed it has nothing to do with him: it is a message to you, enjoining you to deal with a similar negative element - be it in subtlest of forms - within yourself."

Baal Shem Tov (From: Beyond the Letter of the Law by Yanki Tauber)