In Shakespeare's Romeo and Juliet, what are the Nurse's weakest traits as a person or character?
Nurse's weakest character trait is that she is far too compliant. Her tendency towards being overly compliant prohibits her from making morally correct decisions. Although, we can say that her compliance stems from her devotion to Juliet, and her desires to make Juliet happy.
We especially see Nurse be overly compliant when she agrees to act as a messenger to help Romeo and Juliet establish their plans for marriage. While we see Nurse acting in a way that shows us she wants to preserve Juliet's honor as a maiden, she does not stop to think about how unwise and unsafe it could be for Juliet to marry in secret. We see Nurse acting with the intention of preserving Juliet's honor when we see her ask Romeo if his intentions are honorable, warning him that it would be horrible if he broke Juliet's heart or violated her in any way, as we see in her lines:
[I]f ye should lead her into a fool's paradise, as they say, it were a very gross kind of behaviour ... for the gentle woman is young. (II.iv.152-154)
In this passage, the phrase "fool's paradise" can refer to premarital sexual relations. In other words, Nurse is warning Romeo not to try and take advantage of Juliet. When she learns that Romeo does genuinely intend to marry Juliet, without hesitation, she tells Juliet to go and meet Romeo at Friar Laurence's. Also, without hesitation, she finds the rope Romeo will need to enter Juliet's room for their wedding night. Had Nurse been less compliant and less worried about only making Juliet happy, she would have tried to persuade Juliet not to enter into a secret marriage.