As a Teen, many peoples main concern is friends and popularity. As big of a priority this is for teens at school, friends don't last forever. When you leave high school all the people you thought were your best friends will most likely disappear and you will never see them again. I'm not trying to downgrade the importance of friendship, but when you get older there's more important things than your friends.
When you become an adult your world crashes down around as there is no one to support you but yourself anymore. Bills start pouring in food money needs to be saved your rents late, its chaos. Growing into an adult was more difficult for others that were less organized or responsible. Then, when the time comes to have kids you have even more to provide for and worry about.
Helping your parents around the house is a big thing as a teen. Chores on the weekends used to seem like a huge burden but once you hit adulthood you would give anything to change back to just having some simple chores to do on the weekends than sitting in gridlock traffic for your new five to nine full time job. Don't think that your parents make you do chores to punish you they are trying to prepare you by making you responsible.
The differences between being a teen an adult as I've described, are drastic. Without proper conditioning by your parents as a child some people would never make it in the real world as an adult. And some don't that's why we have full prisons and homeless shelters all over the US, so make the decision to start preparing yourself for adulthood, now.