I don't understand myself!

Why am I drinking coffee when I know I shouldn't be? Sometimes I feel like such a masochist, in a sense that I inflict pain (?) on myself when I know it will hurt me, physically. 

Another favorite song of mine: http://www.youtube.com/watch?v=L5_XTnFI6hQ&feature=related

The lyrics are so sad. I guess I can somehow relate it to myself? Same conversation I had, in the same context...