What Makes Us Human

What makes us human? The deep passions we feel for love, or hate? Or is it more, when we love, we set conditions? Or how about when one of our loved ones start to pass away, we want to do everything we can to make it so they don't go, we can't accept our family member or friend might leave of us forever. Because if we accept that they are going to die, then it means we have given up on them, and the life they still could have. Even Christians do it to other Christians, they know they will see them again, but still they can't let their loved one go, because it is too hard to say goodbye, i love you always, and i will miss you something fierce, but go be with God because He is calling you home.
Why is it so hard for some to say? And others it is a simple for them to say?