Shakespeare's Romeo and Juliet is a tragedy, and as such, is not optimisitc. On the other hand, the drama is a realistic depiction of life which inevitably always ends in death. However, it is not appropriate to label the play as pessimistic, either, simply because Romeo and Juliet die. However, if the reader considers the role of fate in this play, an interpretation that includes pessimism is, then, plausible if Fate is an inescapable force.
That Fate is, indeed, a force that exerts its power on the lives of Romeo and Juliet is more than merely suggested in the Prologue to the drama:
From forth the fatal loins of these two foes
A pair of star-crossed lovers take their life....
The fearful passage of their death-marked love,
And, throughout the acts of Shakespeare's play, Romeo senses fate exerting its affect upon him. At the end of Act I, Scene 4, for instance, Romeo tells his friends, who suggest they attend disguised the Capulets' celebration, his apprehensions,
I fear, too early; for my mind misgives
Some consequence, yet hanging in the stars,
Shall bitterly begin his fearful date
With this night's revels and expire the term
Of a despised life,.... (1.4.113-117)
In addition to this circumstance, there are other scenes in which Romeo feels himself "fortune's fool" rather than in control of his life such as when he causes Mercutio's death and then retaliates against Tybalt in Act III.
Juliet, too, seems a victim of fate when her mother announces to her in Act IV that she must marry Paris when earlier her father has turned down Paris's proposal, arguing that his daughter is too young to marry. This new insistence that she marry, of course, places Juliet in the fateful position of being unable to do so because she is already married to Romeo. Thus, the unfortunate chain of events occur as she tries to escape fate. So, if the interpretation of Shakespeare's Romeo and Juliet is that Fate plays a major role in the tragic design of life, then one must conclude that this drama is certainly pessimistic.
William Shakespeare's Romeo and Juliet clearly has an unhappy ending, as summarized in the final lines by the Prince:
Go hence, to have more talk of these sad things; ...
For never was a story of more woe
Than this of Juliet and her Romeo.
On the other hand, we cannot conclude from this an overall optimistic or pessimistic view of life. There are two teenagers in the play who behave foolishly and impetuously and precipitate by their impatience their own deaths. This does not imply though, that everyone behaves in such a fashion and that everyone will come to a bad end. There really is no general position taken about life in general in the play; it is eventually just a story about a specific incident.