The brain, though incredible, will not function as properly as it should if you do not train it to. By training and disciplining the brain or the person from an early age, it is easier for certain norms and behaviors too stick throughout their life. This can be used for better or for worse but it is better to do it young when the brain is still growing. This is because when people age, so does their memory and they would already have their own habits by then.
