You Grow Up but that's all the topic that are discussed elsewhere . here is however:
Everything you do , that you have been doing since you were a kid , has not changed . Your Behavior is same , Even the consequences are same .
Just we don't realize that things have been happening exactly the same way like before when you were a child.
Adults think Adult are smarter. They are not , they are only exerted to interact with other Adults. Same age Groups. There is a reason why Adult-Children interaction is quiet awkward.
If one understand children and adult on the basis of how they get things done, it gets pretty clear. The tactics are similar, consequences are similar relatively.
Punishment are punishments. The physical aspect may look varied but the impact emotionally is same.
Conflicts also arise because it so happens that there is a certain selfishness.
Happy comes from fulfilment and content,for a child and adult.
So what changed? The environment.
Another analogue is that of a person with job and a jobless. Let's take a case where both complete a same task of writing.But due to environment, they are treated differently.
As we grow, our environment is changed with the collective effort of similar aged group people. They have certain type of needs, desires that the needs to fulfil. So gradually the environment is changed. Leaving us wondering, that we are grown up, where instead we are children in context.