The misinformation is definitely a huge part! Especially with things like heroin, kids are always told it'll destroy your life, lose all your money, your family, all you hold dear, ect...

Buuut then they or a friend try it and go "whoa! this isn't so crazy, I'm floating along on a cloud for the whole afternoon, and it only cost a dollar or two"
And with all the misinformation they don't realize how horribly slippery of a slope they're on until they're doing anything for the next hit and its hundreds and thousands of dollars a week because the tolerance explodes up disturbingly fast, and they can't ever stop because they Need it now.