The existence of fate notwithstanding, "Destiny is not so much a matter of chance as of choice" [William Jennings Bryant] in Romeo and Juliet. In several instances, rash judgments are made by each of the young lovers that then determine their "fates." But, it is their choices, not chance, that determines outcomes.
Here are some examples of their choices that effect what are termed "fateful" consequences for Romeo and Juliet:
1. In Act I when Benvolio urges Romeo to attend the party, he has a premonition,
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...(1.4.133-116),
yet, although he may sense fate, he chooses to attend the party at the Capulets.
2. Then, in the next scene, after seeing Juliet he impetuously approaches, declaring his love for her. Risking death, he scales the Capulets' orchard walls and stands beneath Juliet's balcony and they exchange avowals of their love in spite of their awareness of the danger. Romeo defies the fateful consequences that may come by saying,
Alack, there lies more peril in thine eye
Than twenty of their swords. Look thou but sweet,
And I am proof against their enmity (1.5.71-73)
3. When Juliet has some misgivings about becoming seriously involved with Romeo--
Oh, swear not by the moon, th'inconstant moon,
That monthly changes in her circled orb,
Lest that thy love prove likewise variable (1.5.109-110)
I have no joy of this contract tonight.
It is too rash, to unadvised, too sudden,
Too like the lightning, which doth cease to be
Ere one can say "I lightens." (1.5.116-119)--
she ignores her intuitions and chooses to go along with Romeo.
Once Romeo and Juliet have committed themselves to their love despite their intuitive judgments, as in Robert Frost's "The Road Not Taken," "way leads to way," and the sequence of events occur that place them in precarious situations. But, these all come as a consequence of their original choices. For instance,
4. Romeo tries to ameliorate the dispute between Tybalt and Mercutio because he has married Juliet; otherwise, he would have sided strictly with Mercutio and could have run Tybalt off by his having been outnumbered. So, he brings the "fateful" consequence of banishment upon himself. Although he decries, "Oh, I am fortune's fool!" he more honestly blames his having been too "feminine" (weak) in his actions as he tried to appease Tybalt.
5. If, then, he were not banished to Mantua which becomes quarantined, Romeo would know the occurrences at the home of the Capulets. Thus, none of the tragic events of his and Juliet's suicide need happen.
6. In addition, if the children had been forthright with their families and told them that had secretly married with Friar Laurence present, tragic consequences may have been averted. But, they are deceptive and try to manipulate their world to their desires--"Then I defy you, fate!"--When things become out of control, they impetuously end their lives.
Before his play even begins, Shakespeare suggests that all is fated for Romeo and Juliet. The Prologue is the best place to start if you are looking for evidence that fate dooms Romeo and Juliet from the minute the play begins with the reading of the Prologue all the way through the ill-fated plans and mistakes that arrive at the play's conclusion.