Rabbi Noah Weinberg z"l was speaking to a group about judging people to the good. He was asked how to deal with people who seem so negative and evil. He replied, "Imagine you were at a corner ready to cross at a light. All of the sudden from behind someone shoves you into the street. You fall and get up scratched and dirty; you turn, ready to give the person who shoved you some of the angriest words you know. When you turn around, ready to pounce, you see that the person behind you is wearing dark glasses and holding a white cane. How do you feel now? Instantly you calm down, and your anger dissipates. He couldn't help it. he was blind."
"That," Rabbi Weinberg said is how we deal with people who appear to us to be evil and mean. "The person is blind. S/he doesn't wake up in the morning and decide to hurt people that day. The person literally doesn't know what they are doing. They are blind". "The next time your parent, in-law, coworker etc. does something to make you crazy, picture them wearing dark glasses and holding a white cane. They are blind. They can't see that they are doing wrong. Help them, guide them, and show them gently the error of their ways. But don't expect them to change. A blind person can't see overnight. It takes time, and sometimes they will never see."
This is taken from Lori Palatnik & Bob Burg's Gossip.