It is a combination of fate, bad luck, and bad choices that leads to Romeo and Juliet's deaths, and the audience feels both annoyed with them and sorry for them.
The Prologue prepares us for the fact that Romeo and Juliet are going to fall in love and die.
From forth the fatal loins of these two foes(5)
A pair of star-cross'd lovers take their life;
Whose misadventur'd piteous overthrows
Doth, with their death, bury their parents’ strife.
By saying that they are “star-crossed,” Shakepeare is telling us that they fated to fall in love. In that case, they had no choice. The fact that their families were feuding is in some ways bad luck then. Did they find each other more attractive in spite of the family feud, or because of it?
Is she a Capulet?(125)
O dear account! my life is my foe's debt. (Act 1, Scene 5)
There is no real way to tell. We do know that when the lovers first meet, neither one knows who the other is. Thus they were attracted to each other without knowing their love was forbidden, although it is possible that the forbidden love made the love stronger.
There are other instances in which fate or luck play a role. The most notable of which is Romeo’s killing Tybalt. This one event is the one on which all others turn and it was a complete accident. Romeo never had any desire to take part in a fray. He tried to intercede on Mercutio’s behalf and ended up getting him killed. Then he had to fight Tybalt and ended up killing him.
Is but a little way above our heads,
Staying for thine to keep him company.
Either thou or I, or both, must go with him. (Act 3, Scene 1)
Romeo was banished, and he and Juliet had to get married in secret. Juliet’s parents had no idea, so they wanted her to marry Paris. You could argue that there is more than bad luck at play there. If they had listened to their daughter when she said she did not want to get married, it would have saved her life.
Romeo finding Juliet still asleep because he didn’t get the note telling him she faked her death is another case of very bad luck. When Juliet wakes up to find Romeo dead, and has time to kill herself, this is another terrible coincidence.
At the end of the play, the audience feels sorry for the lovers and the parents, but also feels that they all brought a lot of it down on themselves.