I do not understand

I do not understand how one human being can be totally inconsiderate, disrespectful, and negative toward another human being they claim to care and/or love. What happened to do unto others as you would have other do unto you? The world is
basically a jaded, self-centered travesty. Does a relationship have to be jaded, self-centered, hurtful? Why is it so difficult for most to stand up to the world and be humane? Does everything have to be a cruel reminder of man’s inhumanity to man?