Was fate responsible for the tragedy or was it the immaturity and rash decisions of the characters?

Although fate is a theme in the novel, Romeo and Juliet mention it many times, I think impulsive love combined with a disregard for the consequences of their actions are both the tragic flaws for both these characters. Shakespeare had the adolescent brain figured out in the 1600's. It would seem not much has changed. Adolescents are still prone to take impulsive risks today. That's pretty much the major theme of this play.