Rav Erez suggested that the principle begins with a famous Mishnah in Negaim. (That's the masechet that deals with tzara'at.) The Mishnah teaches,
In the context of the Mishnah, we learn from this that a Kohen can declare all incidents of tzara'at as impure, except his own. Yet, commentators have a field day with this Mishnah, and especially the unusual language of רואה, meaning, "he sees," deriving the obvious truism that, "a person sees all blemishes, other than his own." While everyone else can see my faults clear as day, for some reason I can't see them. How true it is!כל הנגעים אדם רואה, חוץ מנגעי עצמו.A man may see every ailment, other than his own.
Yet, Rav Doron answered our lashan hara question by reading the line only slightly differently:
Read this way, the Mishnah communicates an even more powerful truth: when I see faults in others, I'm really seeing my own faults without even realizing it. Others' failures that match our own, trigger an instinctive desire to criticize ourselves. Yet, because I refuse to at least consciously acknowledge my own faults, I can only criticize the faults I see in my neighbor.כל הנגעים אדם רואה חוץ, מנגעי עצמוEvery blemish that a person sees external to him - comes from his own blemishes
Why can't we - or at least won't we - see our own failings? That's due to a deeper problem. Quoting Rav Nachman of Breslev, Rav Doron said that deep down, we won't look at ourselves because we really believe that we're bad. We're evil. So I don't want to look at myself, because I'm afraid of what I'll truly see.
But, said Rav Nachman, we're wrong. We're not evil. In reality, we're good - very good, and our failings stem from an unwillingness to believe in and look at ourselves. Because if we really thought that we were good, we'd have no problem seeing the "dirt" in our personalities and trying to clean it. After all, I'm generally clean. All I need to do is brush off a little "stain." But because I think that I'm really bad, I don't even want to look at myself in the mirror, so I look at others around me. I see my own failings in them. And I speak loshon hara.
What's the solution? How do I stop speaking slander about others? The first step is seeing the good in myself, and understanding that we really are good people. This, said Rav Doron, is actually a verse in Tehillim that we all know by heart.
Again Rav Doron reread the first verse:מִי-הָאִישׁ, הֶחָפֵץ חַיִּים; אֹהֵב יָמִים, לִרְאוֹת טוֹב.נְצֹר לְשׁוֹנְךָ מֵרָע; וּשְׂפָתֶיךָ, מִדַּבֵּר מִרְמָה.
Who is the man that desires life, and loves days, that he may see good therein?
Keep thy tongue from evil, and thy lips from speaking guile.
מִי-הָאִישׁ, הֶחָפֵץ חַיִּים, אֹהֵב יָמִים - לִרְאוֹת טוֹב
Who is the man that desires life and loves days - let him see the good!
If we want to keep our tongues from evil and stop saying lashon hara we must first fulfill the previous verse: לראות טוב - to see the good within ourselves. Once we understand just how good we are, we can aspire to imagine how much better we can truly be.