Why does Tamagotchi lose discipline when it grows?
This is normal. Each time your Tamagotchi grows into a new stage, he usually loses some or all of his discipline. Maybe it is like how people gain more freedom as they get older, and as they gain more freedom they must learn to be more responsible and well-behaved. When your Tamagotchi grows, and it loses discipline, do not worry! You will always have the chance to discipline it more as it grows.