Is Purgatory Like a Diet?

I've heard it said that the purpose of purgatory isn't to punish you for what you did here on earth, but rather to cleanse you of attachment to sin. Saturday I signed up for Weight Watchers. Those of you familiar with the program know that they talk a lot about lifestyle changes, about learning a new way of eating, and about how to be successful at not only taking the weight off but keeping it off, you need to not think of it as a diet that you go on and then off, but rather a new way of looking at food. I've said before that if I preferred salad and exercise to dessert and web surfing, I wouldn't have a weight problem. Maybe purgatory is something like that. Here on earth we work to conquer certain sins--but some of them we'd really rather keep. Through grace, motivation, will, or some other force, we may manage to avoid them for a while, because we know we should--but we are still attached to that sin, we wish we could do it, even if we choose not to. In the long run though, we need to lose our attachment to that sin, just as I need to lose my attachment to bad eating habits--and that's a hard thing to do.