Think outside yourself. Every person has a unique childhood, a unique set of traumas, unique mental health issues. There are many people not lucky enough to be born as intellectually or emotionally intelligent as you were, not lucky enough to have an upbringing like yours. You have no idea what kind of grief, heartbreak, or other misfortune another person may be suffering through. However awful someone is acting, it would probably make a lot more sense if you could spend a few minutes inside their brain.
