Your right they cant
1 John 3: 8 He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil. 9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
Heb 10: 14 For by one offering He has perfected forever those who are being sanctified.
phil 1: 6 being confident of this very thing, that He who has begun a good work in you will complete it until the day of Jesus Christ;
you see unlike you I believe in the power of God, and that it is his work, not my work, that is my sanctifying power, because of this, as a child of God I can’t revert to going back, because it is God who is working, if I fail, God failed to do what he promised, and that’s on God,
my God does not fail I am sad you think yours can