To truly understand people, you will have to invest enough time into them to learn their backstory.

If you knew how her parents treated her, her depressed attitude would not surprise you anymore.

If you knew how his first wife spoke to him, you would understand his constant anger.

If you knew about the cancer he survived ten years ago, it would be clear why he was such a grateful person.

If you knew about her multiple miscarriages, maybe you would understand her absolute love for working with babies.

Instead of spending your time and energy trying to figure them out, psychoanalyzing them, or gossiping about them, it is far more productive to get to know them and their backstory. Maybe then you will come to appreciate them and understand their actions just the way people have done with you.