"WHY DID YOU DO THAT" - "IDK"

I have always wondered why teenagers do the things they do.

Like, why would you smoke when you know the harmful effects it has on your lungs. Or why drink, when you know the legal drinking age is 21.
'It's Because Teenagers have a defect in their brain, that causes them to have impair their ability to reason, and think of consequences.

http://www.pbs.org/wgbh/pages/frontline/shows/teenbrain/