With frequent confession and Mass/Communion, combined with a LOT of prayer, we CAN overcome, unless we have allowed ourselves to become totally possessed. A long history of habitual sin does seem to result in demonic forces being able to sink their ‘tentacles’ into us, deeply in some cases. Turning away from such a way of life and living a devout life can be terribly hard, but in such cases, I believe God assists us, revels in our struggle end eventual victory, and even allows us to bear some fruit in the process.
Someone in the Spirituality section mentioned the Manual of Indulgences recently. I have ordered a copy. Not to be used as a catalog to pick and choose the right buttons to push for my salvation, but rather to use as a guide toward maximizing my prayer life, and putting as much weight as possible behind the life I have come to live.