“The man of knowledge must be able not only to love his enemies but also to hate his friends.” ― Friedrich Nietzsche.
Sounds confusing, but an explanation below: For me this quote by Nietzsche is addressing true objectivity.
Think of the “man of knowledge” as a referee in a football game. They love one team and hope that team will win.
But they have to be fair.
They can’t let their “hatred” of the one team or their love of the other influence the truth of a call. In this case they must learn to ‘love their enemy” (the other team) and “hate their friends” as a metaphor for the difficulty in staying in “What is true, regardless of your relationship to either side”.