Everyone plays favorites, whether or not they admit it. I'm not talking low-stakes this-or-that affairs either, like your favorite food or color of the rainbow. Those are the “favorites” that folks are expected to have. There's a dirtier subclass of favoritism in this world, a collection of hairs people prefer to leave unsplit or pretend as though they have.
It's very possible your greatest lover isn't your current partner. One of your students might be positively brilliant and make your other earnest pupils seem worthless. Your father might not just be the “bad guy” in the relationship, but a legitimately bad guy.