At war with others

I read something in one of my horoscopes,

"If you're at war with others, you're never at peace with yourself."

I completely understood, but I find this intriguing.

Example for someone just out of a bad breakup: Is it fair that someone can treat you so badly and then just move on and be happy? This makes you "angry" and "at war" emotionally, so can you find peace? I think this comes with time. I think this statement is so true, but it's not always available right away.

What does this statement mean to you? Can you relate?