We want what we can't have

Why do we always want what we can't have? For some odd reason people desire a hundreds times more what seems to be impossible rather than what is tangible. For instance, let’s suppose you eye a guy in the club and you’re instantly attracted to him, but there's a possibility that he won't acknowledge your presence. As the night goes on he still has no idea you exist and he becomes an obsession for you, so then you'll begin to do what ever it takes to get his attention. Another guy comes up to you and starts a conversation but during that time all you can't think about is the guy that ignores you so you reject this sweet man. You leave the club disappointed because after all your persistence you still couldn't get him notice you. Why does life have to be so complicated sometimes? I guess that's how it is and there's is nothing you can do to change the way of life but accept your loss. It pisses me off because it's like you can't be with the person you truly like and instead you're stuck with the person that you perceive as a friend. It's sad because these situations happen often and in the end there's nothing that will get his attention. I mean, we can walk around half naked and he still won't turn around. How depressing. Then again, maybe when this happens, it's not meant to be. Things do happen for a reason, which I can't seem to figure out yet. When will be the day when everyone finds the person that they're truly meant to be with?