As an introduction to his explanation of what has happened, Friar Laurence takes responsibility for part, but not all, of the tragedy. He hopes his words will clarify why events have unfolded as they have:
"I am the greatest, able to do least, yet most suspected, as the time and place doth make against me, of this direful murder; and here I stand, both to impeach and purge, myself condemned and myself excused" (V,iii,223-227).
After hearing what the Friar, Balthasar, and the Page of Paris have to say, the Prince addresses both the Capulets and Montague, effectively saying that heaven, or fate, has been the ultimate cause behind the tragedy, and that because of their hate, everyone, including himself, are convicted and punished:
"Where be these enemies? Capulet, Montague, see what a scourge is laid upon your hate, that heaven finds means to kill your joys with love. And I, for winking at your discords, too have lost a brace of kinsmen. All are punished" (V,iii, 291-296).
Many factors must share part of the blame for what happens to Romeo and Juliet.
1. The family feud led Romeo and Juliet to keep their love secret. All the sneaking around led to the miscommunications (Romeo did not tell Tybalt why he wouldn't fight him, the Friar nor the Nurse mentioned the marriage to the parents, resulting in Papa Capulet being in the dark when planning his daughter's marriage to Paris).
2. Impulsive behavior by the "star crossed" lovers led them to react to situations without thinking first. Count how many times they say that they want to kill themselves throughout the play whenever something goes wrong!
3. Mercutio told Romeo to forget about his bad dream and go to the party. His belief that dreams are nothing led Romeo to go against his gut to stay home. His meeting Juliet sets off the chain of events that follow. Mercutio's hot-headedness that led him to jump in to fight Tybalt when Romeo refused led Romeo to impulsively kill Tybalt in revenge. His banishment left both Romeo and Juliet in an unbalanced state.
4. Fate stepped in to ruin the Friar's plan when Friar John could not deliver the letter of explanation to Romeo. Mr. Capulet made matters worse by bumping the wedding date up, forcing Juliet to drink the potion that same night.
Prince: "See what a scourge is laid upon your hate,/ That heaven finds means to kill your joys with love." (V.iii.302-303)