What I came to notice is that the survival instinct of the life force is very powerful, more powerful than the addiction. If it weren't, addicts would deliberately overdose much earlier into their addiction just to get it over with. They invite the inevitable. While the life force keeps giving the addict one more chance, he's too wrapped up in his despair that he can't perceive any hope or bear the thought of holding himself accountable. This is why the addiction will eventually overpower the life force.
Addiction just has greater endurance.
Over time, an addict develops such a complex system of denial and self-justification that the subconscious begins to willingly participate in his schemes. The first thing you wonder about when a new inmate comes to stay at your house is if he's going to be a burden to your already troubled existence. If there isn't an immediate bloodbath, new guys are usually left alone until they get into some communal space. Then they are asked what false accusation has been made against them. Since most felons initially claim innocence, simple courtesy demands that you go along with it.