Early Intervention is scary to many parents. In my 24 years of working with addicts and their families I frequently see parents who know their sons or daughters are in trouble with substance and behavioral problems. But it scares many parents to take strong action to get them help.
One barrier to parents taking action is failing to recognize the need for clarity. If a 16 year old or 20 year old is using alcohol regularly or smoking pot regularly many parents will agree it should not be happening but refuse to confront and provide consequences for the behavior.