Walter Kaufmann of Princeton University, where I met him late in his life -- he'd had a long track record before that -- used to quote with approval Nietzsche's advisory: "be a hard bed for your friends."
Now why would anyone wanna be that? Aren't friends precisely those people with a soft lap, more cuddly?
Well, if you think of cop or doctor shows where there's some conflict -- or lawyer shows -- you get the alpha apes playing racket ball.
They're on the opposite side of some issue at work, so there's a plot. They've been at loggerheads before.
That's part of what drives the season (plots involve opposition and tension).
"These two women are friends" (just to go against the stereotype) one soon realizes, yet they're each into trouncing the other in some professionally recognized way, like in sports. Racket ball becomes a metaphor. Or tennis. The CIA executive director (e.g. Nora Slatkin) is always leaving her 7th floor office to go play tennis with the FBI director (DiCaprio?); the spy novels are full of that stuff.
So in that sense I think Nietzsche was saying to be a strong racket ball partner for your friends, like a coach or better, a sparring partner. What better way to develop your immune system, your defenses, than by working out against a lesser enemy, i.e. a friend. I know it sounds weird to put it that way, which is why I did so on purpose.
When you have someone's interests at heart and yet appear to present obstacles, you're in well known territory where storytelling is concerned.
Married couples often confuse themselves in not recognizing that they're also racket ball partners i.e. well positioned as trainers to play hard ball in such a way as to improve the others' performance. That's the theory anyway. The mindset to adopt is your opponent is not "unfair" or "out of line" but "highly paid by invisible others to serve just exactly in that way". That's a meditation, like when the Dalai Lama says to imagine everyone as your mother. I'm not trying to make you paranoid.