How do you handle a situation where the data suggests one path but your understanding of human nature suggests another?

Why do you think some people can’t let go of historical grudges, even when living in a different country? Have you experienced this?
Have you ever regretted a decision you made in a relationship that affected your friendships? How did you deal with that regret?
What do you do when a friend's family member acts bigoted towards you, but your friend doesn't share those views?