Once you truly understand someone they will never upset you again. Once you truly understand yourself you will never feel invalid again. Understanding leads to compassion, compassion leads to forgiveness, forgiveness leads to acceptance, acceptance leads to freedom.
People aren't hard to understand. We're all struggling with ourselves in some way. We all feel intrinsically invalid in some way, we all want to feel valid. ALL unloving behaviors are about trying to manage this inner conflict. Accept that, and love for others, for yourself is inevitable. It's only our resistance to no longer using someone else to justify our own feelings of invalidity that prevents us from freeing others from judgement and being free ourselves. We stubbornly want anyone, anything but ourselves to be responsible for our pain.
All suffering is thus a self created prison. That's the tragedy of it. It's also the beauty of it. You can let go, open the door and leave at any time.