Dysfunctional family, lack of friends (either their own fault or the other party resulting in being antisocial usually) peer pressure, abuse of any kind (sexual, physical, emotional) lack of a parental figure (in my sons case its due to his birth father disassociating himself from all of his kids) so abandonment issues, needing an escape from what theyre totally over analyzing everything due to hormonal issues, u may also consider them growing up in a house where it was used frequently right in front of them