Vayeitzei, 29:7. Guests who give mussar.

The Ohr Hachayim says (on Vayomer Hein ohd hayom gadol ) that Yaakov was giving the local shepherds mussar for waiting so long to water their sheep. He acted in this judgmental manner, despite having just then arrived, because inflicting pain on animals is prohibited in the Torah. The Sforno addresses the same issue by saying that “Hatzadik yim’as es he’avel gam kein el ha’acheirim, ” a righteous man will despise iniquity in others as well as in himself. The point is, that both meforshim felt it necessary to explain how it was that as soon as Ya’akov came to the land of the B’nei Kedem that he could ‘musser’ them about their affairs, and they both answer that this was because of the intense feeling he had for the perceived injustice

The perspective of a visitor is valuable, because he will see things that the regular residents don’t see. Community members are inured to the bad habits that develop incrementally, and they can’t possibly see them without help. Who appreciates the observations of a visitor, the mussar that he gives you? Only a yarei shamayim who is not a ba’al gaavah. If he is sincere in his avodas Hashem, and he doesn’t have a chip on his shoulder, he will listen and weigh the musser of the visitor. To highlight this idea, consider the contrast to the attitude of the people of Sdom, who said to Lot, “Ho’echod bo lagur vayishpote shafote.” Of course, sometimes the visitor is an overconfident boor or a naive little pisher, and the people are right to be offended.  But at least, listen to what he has to say without immediately dismissing his observations.