What is the point of punishment? all it does is makes a person suffer and be misreable?

i am on punishment for a whole month, i am confined to my room every weekend until July, i am only allowed out for school , my crime i sneaked out while grounded and got drunk with some friends and throw dustbins around the police came and took me home to my parents, they went mad and said i must expect quite a severe punishment, i have been shut in my room all weekend and i have another month to serve, i have told my parents i won't do it again so why do i have to suffer being punished all it does is make me misreable?
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my parents are having a barbecue party on Saturday, my cousins are coming and it sounds like a great day, my parents said because there will be alcohol at the party and plus i am on punishment, i will have to stay LOCKED in my room for safety reasons as well as a punishment , i think this is really cruel what do you think, please be honest?
my older sister says i have caused much worry for my parents and i deserve to be locked in my room and punished ADVICE PLEASE?
What is the point of punishment? all it does is makes a person suffer and be misreable?
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