One of my favourites (edited):
We all want things that we know are bad for us. Everyone has dangerous fascinations and unhealthy fixations. Some of them are a little harder to explain than others, but most of us know how to keep our impulses in check, we use willpower to fight off our darker instincts. Unfortunately, for others willpower just isn't enough. The siren call of one's own obsessions is simply too strong to resist. The thing we used to want becomes a thing we now need. Our obsession becomes our compulsion. Until we realise, pursuing the one thing we want most in life has left us without much of a life at all. But in the end, the compulsions are still there taking us to ecstasy or pushing us over the edge to the brink of death.