1) The tragedy of Romeo and Juliet is caused by their impulsive actions and stubborn natures combined with bad luck and miscommunication.
2) Romeo, upon hearing of Juliet's death, impulsively buys poison from an apothecary and goes to her tomb to die with her.
3) At the tomb, Romeo encounters and kills Paris before drinking the poison just as Juliet awakens; she then kills herself with Romeo's dagger so they can be together in death.