It turns out in the end, we are solving problems for real people, and so all the messiness of real people: the pettiness, the tribal nature, the bickering, the facts-bent-to-justify-feelings... That's in the problem domain.

(For software engineers in particular, who can trend towards wanting to think of themselves as little logic-machines divorced from that kind of behavior: I also think it's a good exercise to keep that stuff in-scope because we are not immune to our own humanity, and recognizing when others are being tribal and petty makes it easier to recognize it in ourselves.)