What do we learn from "Al Tetzei la'Riv Maher..."?
Sanhedrin 44b: When Hashem told Yechezkeil to tell Yisrael "Avich ha'Emori v'Imech Chitis", a Ru'ach Poskanis (angel) asked, if Avraham and Sarah would come in front of You, would You embarrass them this way?
Malbim: All man's actions must intend for the end that will come from them. He must not do an act that will cause the opposite of what is sought. If one disgraced you, do not rush to quarrel, thinking that this will return your honor, which was disgraced. A quarrel will not attain this, rather, the opposite. He will disgrace you a second time via the quarrel! In place of restoring you honor, you will get shame and disgrace.
What is the meaning of "Pen Mah Ta'aseh"?
Rashi: Lest you come to a state in which you do not know what to do in the end.