On Sadness (or) *tear tear*

Here's a question I just have to ask; what makes things sad? I mean, not just "oh, that sucks" type sad, but like, the deep, personal type of sadness. When you're touched so deeply, in a place where your normal life never comes close to reaching, that even if what touched you is happy or good, you still become sad. It's like at the core of each of our beings is a bundle of sadness, and we don't even know it's there. But anyway, really, What makes things sad?
There are some things that will touch people repeatedly or with the same or similar reaction. Some songs will do it, (for me it's Hallelujah by Rufus Wainwright) and other times it is a certain poem, or movie sequence, or picture, or something else entirely. It just has to be something that reminds us that we are alive, life is filled with pain, to feel it is normal, to not ever cry from the sheer agony of being alive is insanity, and most importantly, Love Hurts, because what we are at the core of our beings is love and sadness. When we are reached, touched deeply by something, tears (a basic signal of sadness/strong emotion) are almost always a part of the experience.
But, again, what makes things touch so many different people? There must be some kind of equal imprint upon us all, to make the same song, or poem or painting or whatever it may be have such a strong effect on thousands of us humans. I think that one of the basic ways of defining humanity must be the effect of Art. Even if computers were capable of making advanced, autonomous decisions, they wouldn't be human if they didn't cry at the sound of heartbreak, in fact, to truely be human, you must be moved. There is evidence that poetry is a natural, instinctual form of art, and this must be true. No matter how scientifically advanced a civilization is, if they are not moved by emotion at the core of their beings, they are not humanity.