The practice of law teaches us a very important lesson. The primary pursuit of an attorney is the search for evidence that will exonerate his client. Whatever the circumstances and however flimsy the case, the lawyer puts all his efforts into building a defense. In like fashion, each of us should attempt to find all that is good and worthy in our fellow Jew.
If one digs for water and doesn't find any, this does not mean that water isn't there. One must dig deeper in order to find the source. The same principle applies to seeing good traits in another person. Although these may not be readily apparent, if one looks with honesty, he will certainly find positive attributes in his fellow. If, in the end, a person can only see negatives in others, this suggests that the deficiency actually lies within himself. This is closely related to one of the key precepts of Judaism - to judge others favorably and to always ascribe good motives to their behavior.
Sichos Kodesh of the Rebbe, Acharon Shel Pesach, 5714