Everyday you hear bad news about drugs. Maybe even see bad stuff happen to people. Everyone knows that drugs are bad for you. They just aren't good things to do. But people still use them.
People try drugs for all kinds of reasons.
No one wants to be the only one not participating. No one wants to be left out. No one wants to be seen as a loser or a nerd. So they make bad decisions, like taking drugs, to cover-up their insecurities. They forget that there's nothing more loser-ish than losing control at a party or screwing up a potential date or decent report card because you're hung over.