This is the essential evil of vice: it debases a man.

The real cost of a bad habit is less the outward damage than what it does to your sense of yourself. Harm to health or money is measurable and often survivable; the quieter loss is that you start regarding yourself as someone who does this, and that lowered estimate makes the next lapse easier. That spiral is the mechanism. It is also why shame works so badly against it, since shame lowers the estimate further.

If you are trying to leave something behind, aim at the self-account rather than at the behaviour alone. Collect evidence that you are the kind of person who does otherwise, in small and frequent amounts.