A wonderful piece by Ed Welch offers some thoughts on this profound question. Welch writes that there are two patterns:
1. Confess—then ignore. A couple indulges in premarital sex and feels guilty. They confess it to the Lord, and promise God and each other, never to do it again. But it happens again, and then again. By the third time they are not quite sure how to proceed. They still might feel a little horrible, but why bother confessing something that you know you will do again? They know that making guilty promises doesn’t work and, by this point, they admit that such promises are lies anyway. They expect to do it again. Better just to let this phase run its course, they conclude. Marriage might come soon, or maybe the sin will gradually die out. Then they can re-engage with God.
2. Confess—try—feel really bad—be hopeless—try to ignore. This is a slight variation on the first and takes a little longer to spiritually quarantine the recurring sin so that no one messes with it anymore. For example, someone might not be planning his next descent into porn, but he has done little to interrupt that descent such as share his internet activity with an accountability partner. He can confess his next nine falls (leaps?) into porn, but once it gets to double digits he starts to wonder, what’s the use? Then this sector of life gradually closes to divine activity, though those bad feelings never quite go away.
The article is helpful for those counseling and for those tempted to do what they know to be wrong.