My father suggested a beautiful idea to me and I wanted to share it with everyone else.
In Deuteronomy 27: 24, the verse reads:
כד. אָרוּר מַכֵּה רֵעֵהוּ בַּסָּתֶר וְאָמַר כָּל הָעָם אָמֵן:
Cursed be he who strikes his fellow in secret. And all the people shall say, 'Amen!'
Rashi to this verse expounds:
מכה רעהו בסתר: על לשון הרע הוא אומר. ראיתי ביסודו של רבי משה הדרשן י"א ארורים יש כאן כנגד י"א שבטים וכנגד שמעון לא כתב ארור לפי שלא היה בלבו לברכו לפני מותו כשברך שאר השבטים לכך לא רצה לקללו:
He strikes his fellow in secret: This refers to evil speech. I saw in the Yesod of Rabbi Moshe Hadarshan that there are eleven curses here, corresponding to eleven tribes. But by Shimon there is no curse because it was not in Moshe's heart to bless him before his death like he blessed the rest of the tribes; therefore he did not wish to curse him.
Look at the wording here. It does not sound as though God told Moshe not to bless Shimon; rather, this was something that Moshe himself could not do. שלא היה בלבו לברכו - It was not in his heart to bless him. It was Moshe who could not bless the tribe of Shimon. If you consider what kind of pain that tribe caused him, it is not surprising. After all, Zimri mocked him publically, stating, "And did you not marry the daughter of a Midianite?" before cohabiting before all with Kozbi.
The suggestion is that Moshe could not forgive this. This point is given even more credence when you realize that the Daughters of Tzelafchad specifically pointed out that their father died in his sin- see Numbers 27: 3.
ג אָבִינוּ, מֵת בַּמִּדְבָּר, וְהוּא לֹא-הָיָה בְּתוֹךְ הָעֵדָה הַנּוֹעָדִים עַל-יְהוָה, בַּעֲדַת-קֹרַח: כִּי-בְחֶטְאוֹ מֵת, וּבָנִים לֹא-הָיוּ לוֹ. 3 'Our father died in the wilderness, and he was not among the company of them that gathered themselves together against the LORD in the company of Korah, but he died in his own sin; and he had no sons.
You know why the Daughters of Tzelafchad specified that? Abarbanel to Numbers 27: 1 explains their thought:
ואמרם עוד והוא לא היה בתוך העדה הנועדים על ה' בעדת קרח היה להגיד שאביהן לא היה בעדת קרח כדתן ואבירם המורדי' עד שתענשנ' בנותיו בעונו על דרך פוקד עון אבות על בנים כי בחטאו הפרטי מת ולא בעונש כללי בתוך העדה החטאי' בנפשותם ולא אמרו זה כפי הדין כי הנה עובדי העגל מתו ובניהם ירשו הארץ אבל היו נשים וחשבו כי בזכרון הזה ימצאו חן בעיני משה לומר שאביהן לא היה בעדת קרח שנועדו עליו.
The reason they specifically explained their father had not been part of the Congregation of Korach but had rather died in his own sin was to gain favor with Moshe: וחשבו כי בזכרון הזה ימצאו חן בעיני משה לומר שאביהן לא היה בעדת קרח שנועדו עליו. They thought that by stressing that their father had not been one of the people who joined the Congregation of Korach and had rebelled directly against Moshe they would gain favor in Moshe's eyes; the implication is that otherwise Moshe would not have been as willing to hear them due to the fact that their father would have been one of the people who personally rebelled against him and hurt him.
What this suggests is that if a person has struggled and struggled within himself to try to forgive someone who wronged him and is not successful, all is not lost. Such a person finds himself in the same position as Moshe, who could not find it in his heart to bless the tribe of Shimon. In such a case, while he did not bless Shimon, he did not curse him either. Let us be content, then, not to wish the person any ill even if we cannot forgive them.
Obviously, the ideal is for us to be able to forgive everyone, to love them and to shower them with blessings. But in some cases this is impossible. In such cases, let us not actively wish them any ill and perhaps we may even hope for their happiness while recognizing that everyone has their limits. I am not automatically a bad person if I cannot forgive someone, assuming I have tried to do so. I simply find myself in the same situation as Moshe- and there ought to be no shame in that. I offer no curses, I wish no one ill- but I cannot forgive. Moshe was publically humiliated, embarrassed and shamed by Zimri- public humiliation is considered a kind of death. But why did he extend this anger with Zimri to the entire tribe of Shimon? Some commentaries answer that Moshe would have loved to bless the tribe of Shimon but they had not yet rectified the qualities that made them dangerous, the ones the tribe of Levi shared and had worked on. And I'm sure that's a valid answer. But there's also the human side to this- Moshe could not bless a tribe that had not defended him or protested against Zimri's accusations. Or perhaps the two are linked- the fact that the tribe had not acted as they should demonstrated that they had not yet redeemed this quality that Yaakov their father had recognized was their downfall. Levi had done so; they had learned to channel it for God. Shimon had not. But the fact that Moshe was a man who could be wronged and who could feel wronged and act on it is demonstrated by both this situation with Shimon and the thinking of the Daughters of Tzelafchad. Even Moshe struggled when it came to forgiveness and thus we can take comfort in the fact that we are not automatically bad if we can't forgive.