How to apologize correctly. This is phrased in the context of marriage, but I think these rules of thumb are important for any kind of relationship with another human being. I struggle with a lot of these; it's a harsh, but nice, reminder to be a better person.
"Too often we don't realize what we have until it's gone. Too often we're too stubborn to say, 'Sorry, I was wrong.' Too often it seems we hurt the ones closest to our hearts, and we let the most foolish things tear us apart." Unknown - www.purposefairy.com/7597/be-kind-what-goes-around-comes-back-around/