What is the saddest fact that was learned about fellow human behavior from your experiences?

What is the saddest fact that was learned about fellow human behavior from your experiences?

One of the saddest facts about human behavior is the capacity for cruelty and violence towards others. Throughout history, humans have inflicted immense suffering on one another through war, genocide, and acts of terrorism. Additionally, discrimination and prejudice continue to be pervasive in many societies, leading to inequality and mistreatment of marginalized groups. The fact that human beings are capable of committing such atrocities against their own kind is a deeply tragic aspect of human behavior.