Why do we do things to hurt ourselves?

Why do we do things to hurt ourselves? I think we all have a little masochist in us somewhere. For instance, why do we look at pictures of people we miss? Because we want to see them, because we love them, etc, etc, etc...all wonderful things; but in the end, sometimes it just makes us feel WORSE. "Why are they so HAPPY in the pictures when I'm so sad?" It's not fair!! Not only that, but there is this ache at the core of our being that we're all addicted to. It hurts, but we want it to hurt because it reminds us that we do feel something. It reminds us that we love...or loved at one time. I would venture to say that more often than not, most people, despite themselves, would opt to feel pain (on some level) over not feeling anything at all. We can laugh and cry, two things other species on the planet don't do. No girl is going to give up the ability to CRY! This girl surely isn't.