The calamitous ending of Shakespeare's Romeo and Juliet owes more to the forces of destiny than to the effects of human love or to human choice. Human love between adults in relatively "normal" circumstances can be part destiny and part human choice, but considering the youth of the protagonists and the hatred between their families, the role of destiny is far greater than either love or choice. Destiny is in charge because they are too young to resist the urge of love, and yet their families are too mutually hateful to allow for any other ending than bloody calamity.
The enmity of the youths' families guarantees that their love will confront a surplus of obstacles. Shakespeare, through the Chorus, immediately makes clear that destiny is to blame: "From forth the fatal loins of these two foes [i.e., the Capulets and Montagues]/ A pair of star-crossed lovers take their life;/ Whose misadventured piteous overthrows/ Doth with their death bury their parents' strife" (Prologue, lines 5-8). The stars, or destiny, are in control of the futures of Romeo and Juliet and there is nothing that anybody can do to avert the tragedy. This inevitability is guaranteed by the fact that the people around the youths--their rage-blinded families--who might be expected to provide them with helpful counsel, are, to the contrary, just as ruled by the destiny of vengeance. Instead of helping Romeo and Juliet, the families provide nothing but hopelessness, further isolating the two in their young passion.
Actually, Romeo and Juliet appear more often wiser than their elders, although their wisdom seems focused not on living wisely but on the inevitability of doom for themselves and their love. The play is full of images of imminent doom, as if the lovers recognize on some innocent level that their love is too pure, too great for not only their families and Verona, but the world. As Romeo says of Juliet: "O, she doth teach the torches to burn bright!/ It...