Repentance does not mean you simply stop sinning. It means, rather, by the grace of God, turning to the only one who has the power to enable you to do so. Being a Christian is not a self-salvation project but an appeal to the grace of God in Jesus Christ as our only hope. Otherwise, left to ourselves, none of us could change. EVER. No amount of therapy or will power could help. Before Christ opened our heart to the gospel, we are all caught in ways of bondage that we could not change. If we could change ourselves we would not need Christ. Part of the problem is that people are still stuck on trying, at least partly, to save themselves. But what is impossible with man (faith, repentance) is possible with God. (Luke 18:27)
Jesus said to them, "It is not the healthy who need a doctor, but the sick. I have not come to call the righteous, but sinners."
Just like you don't need a doctor unless you are sick, in a similar way you don't need a Savior unless you are a sinner. Jesus came to save those who know themselves to be sinners. Man is naturally proud and does not want to admit he is a rebel sinner in need of rescue. In context to the above quote the Pharisees are questioning Jesus as to why he eats with tax collectors and sinners. Thinking themselves more righteous than the rest, these Pharisees are revealed to be people who do not admit they are sinners in need of grace, but proud and think they deserve God's favor. So the call to repentance begins with acknowledging that you are caught in sin, incapable of freeing yourself from its' captivity and an appeal to Christ alone for deliverance from sin's guilt and power.