Years of being marginalized as a kid, noticing that it was sometimes other people being marginalized, wanting to not do that to them myself, recognizing how every interaction has a dimension of social valuation. Mostly.

Much of it is from having an emotionally unsupportive home, and a school environment where the whole cast of characters could change every few years, so for the sake of my mental health I had to get good at making friends.

Maybe some of it is from reading a lot and being a lot better at listening than talking. Maybe I was better at listening because I wasn't such a great conversationalist because my world was oriented around books and games and stuff more than organic human interaction. Maybe good fiction is something that improves your empathy by putting you in a different person's shoes.