Why can't I stop a sin even though I know it is wrong?

Human nature is so beat up and bruised and disfigured that we need the indwelling of the Holy Spirit, God's Spirit dwelling within us, activated with great power, in order to keep us from sin. This is why, when someone comes to me as a priest and they say, Father, I cannot overcome this particular sin, the answer is not to tell them, well, don't do that sin, because that would be ridiculous. If somebody came and said, Father, I can't stop drinking to excess, we wouldn't just give them a command and say, well, stop doing that, stop drinking to excess. I mean, that would be redundant. They already know that they shouldn't be doing that. In fact, their whole struggle is they can't stop doing that. They feel powerless over this sin. So the law of telling someone not to do something is not enough to actually keep them from sin. This is why we always say, increase your spiritual life, increase your life of prayer and of confession, seek to receive from God the power that you don't have in and of yourself, which is the power of the grace of the Holy Spirit. This power dwelling, or working on us and working with us and working in us, is what alleviates both the desire for sin, but also keeps us safe from it. We remember this in the life of Saint Mary of Egypt. This is probably one of the most perfect and profound examples: that even after she went into the desert, was she free of all temptations? And the answer to that is no. We read her life every single year, and she says that she would have the temptations that would come upon her. She had lived a very licentious life, full of a lot of different types of iniquity, and she said that the desire for wine would come upon her, and to sing songs, and to gratify the flesh. And what is her answer to that? Her answer to that was, she said that she would throw herself onto the ground and begin to pray and ask God's mercy, so that he would have mercy and alleviate this. And she says she would not get up from the ground until the temptation had passed. She did not have the strength in and of herself to overcome the temptation. It was too much for her to bear, but rather she relied, through prayer, through prostration, through fasting, obviously, because she was fasting all the time, to seek the help of God, that he would alleviate, that he would remove the desire for sin.