The Vilna Gaon asks: Is hatred ever for nothing? Isn’t there always a reason for hatred? Someone embarrassed him, harmed him, or did something else to anger him, so why is it called sinas chinam?
The answer is, whatever occurred, it was destined. Nothing happened without Hashem’s decree.
So there is never a valid excuse for hatred. ~ R’ Elimelech Biderman Shlita
Emuna Daily 
This seems contradictory – can you explain?
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Meaning, there is never a reason for hatred because anything that happens to you is from Hashem. Even when people wrong you, they are just agents of Hashem. It is all calculated. Hashem will certainly punish them for what they did wrong, but the wrong that happened to you was still meant to be and all from Hashem. Therefore, there is never a reason to hate anyone. Such hate would be baseless! Does that make sense?
I heard a saying
It wasn’t them- its all from Hashem!