We claim to fully understand what we have only partially experienced, and we dismiss other people's reality as invalid if it contradicts our own. That's our ego playing tricks on us until we argue and fight to prove that we are right by making someone else wrong. Yogananda called it "Feeling tall by cutting of the heads of other men." The entire concept that you are somehow separate from others is an illusion. We are here to snap out of our self-importance.