Caring --> Not Caring

I asked someone tonight how one goes from caring for someone to stop caring for someone? Their reply, "because they didn't care in the first place." Awesome. Why didn't they care? How do you have a relationship with someone and not care? I wanna know how to do that! Even people I don't like, or strongly detest, I still care about. I don't wish harm upon them and am sad when they experience illness, job termination and the like. Alas, why do they not care about others? How self-absorbed could you possibly be? If you don't care, then you are just using people to meet your own needs, and then once they're no longer of use to you, they can be cast aside like a piece of trash - never to be thought of again. Like the flowers of the ground, when the wind carries them away, the ground remembers them no more. I am a flower... lost to the wind.