Believers need to understand what salvation really is! That God has killed the old person we were before Christ, not symbolically, but literally, and then He raised us from the dead and seated us with Christ in heaven. We don't need rules or principles or self-discipline!
God dealt with the heart of the matter, literally. In salvation, He gave us new hearts, not hard as stone, but soft as flesh.
Self-discipline is nothing more than a work of the flesh and sooner or later your flesh will get tired of trying to be good (out of pride) and will want to act like itself. Self-discipline only lasts a season!
You see, Christians believe they cannot trust themselves with freedom, because they believe they are still sinners at heart and therefore they renounce the freedom they have in Christ, and in doing so, they remain as children, never moving on to maturity! "O foolish Galatians!"
My point is this: You can trust your heart. It is no longer deceitful, but God has performed a spiritual surgery of the heart. Your heart is no longer filled with sin, but with light, righteousness, purity and self-control. The Holy Spirit brings you freedom from sin IN freedom! You are free to sin, but Christians are not sinners! They died to sin and came alive to God! So the fear of licenteousness because we are not under law has absolutely no basis!
You don't have to discipline yourself anymore. The Holy Spirit, from the inside, will produce self-control in you. You're free to stagger and stumble on your way towards learning to walk upright as a fully mature child of God. Your Father isn't frustrated with you when you fall. In fact, you're not seeing Him clearly if you see Him like that! He is full of delight with you as you learn to walk. He doesn't notice how many times you fall, but He takes notice of how many steps you make.
He coaches you, encourages you and strengthens you with His love. He never discourages you or rebukes you. He is never angry with you.