A character flaw is a defect or shortcoming in a person's character. It relates to the person's inability to perform or not to perform as expected or to do or not do something with regard to the expected norms prescribed by society. Fate is deemed to be one's destiny - events which are outside our control and are believed to be governed by supernatural forces.
In Romeo and Juliet, our two unfortunate protagonists are guided by both destiny and the deficiencies in not only their characters but also in those of other characters. The prologue before Act One makes it clear that it was fate that intervened in the lives of these two tragic souls.
Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life;
Whose misadventured piteous overthrows
Do with their death bury their parents' strife.
The words in bold clearly indicate that Romeo and Juliet were caught in circumstances beyond their control. They were born into families who bore one another an 'ancient grudge' - it was an ingrained hatred which existed since long before their birth. Secondly, the phrase 'starcross'd' suggests that they were destined to meet since it was foretold in the heavens. This, furthermore, means that their joint destiny was irrevocably tied to their circumstances. There was no escaping it and this, ultimately, probably played the most important part in their doom.
There were, however, other factors which added to their eventual downfall, such as their own shortcomings. Both were much too impulsive and took rash decisions, which not only compromised their situation but that of others as well. Their behaviour was irresponsible and naive for they chose to completely ignore the dangers they put themselves into. The tempestuous flame of their desire made them behave in an irrational manner and could have dire consequences, as friar Laurence points out to Romeo in Act 2, scene 6:
These violent delights have violent ends
And in their triumph die, like fire and powder,
Which as they kiss consume: the sweetest honey
Is loathsome in his own deliciousness
And in the taste confounds the appetite:
Therefore love moderately; long love doth so;
Too swift arrives as tardy as too slow.
The friar, in his desire to do good and resolve the lifelong feud between the Capulets and Montagues, also exposes some of his own character defects. He is, probably against his better judgement, also much too impulsive in suggesting that he will marry the two lovers in order to resolve the families' conflict. He is also naive in believing that marrying the two will, in fact, resolve the problem. It is his kindness and an ensuing act of fate, which results in the deaths of the two youngsters.
At a crucial time in the play, the friar's desperate message to Romeo about Juliet's supposed death does not reach the young Montague. The messenger had been delayed due to his incarceration to prevent the spread of the plague as indicated in the following extract from Act 5, scene 2:
FRIAR LAURENCE
Who bare my letter, then, to Romeo?
FRIAR JOHN
I could not send it,--here it is again,--
Nor get a messenger to bring it thee,
So fearful were they of infection.
Therefore, Romeo did not know that his love was still alive and, believing that she was dead, he committed suicide and she did likewise on discovering her lover's dead body lying next to her.
Also, both Mercutio (Romeo's friend) and Tybalt (Juliet's cousin) both had character flaws, in that they were quick-tempered and eager to fight, which added to the drama. Their irrational acts, driven by fiery passion, directly resulted in Romeo's banishment at the risk of execution. Mercutio attacked Tybalt in defence of Romeo for he thought him a coward when Tybalt challenged him. Romeo's intervention in the fight led to Tybalt gaining an advantage and killing Mercutio. Romeo later took revenge by killing Tybalt, an act which resulted in his expulsion from Verona. This obviously complicated matters tremendously.
The heads of both the Capulet and Montague families also had weaknesses which led to their children's untimely demise. They were stubborn and apathetic in resolving their feud and allowed it to fester and then explode onto the streets of Verona, instead of acting in a mature fashion and finding a solution to their fight. It is only after their children had paid the ultimate price for their recalcitrance, that they wiped the slate clean and buried their, by then, grossly bloodstained hatchets.
Finally, Juliet's nurse also had some shortcomings of her own which led to the tragedy. She, as much as friar Laurence naively believed that she was doing good by acting as a go-between for the two desperate lovers. In fact, her and the friar's behaviour only encouraged the two. It was their desire to please which was their unfortunate flaw. The nurse was almost obsequious in her desire to fulfil Juliet's every wish. It would have been much better if both adults had taken a firm grasp and took control of the situation, instead of allowing two lovesick youngsters to rule them without compunction. That was their greatest failure.