In Act IV, Juliet deceives her parents, Nurse, and Paris. Does her deceptiveness comes naturally, or is it born out of necessity?
In analyzing a character, the reader should always look for inconsistencies. And, in Act IV, Juliet's behavior is inconsistent with her actions and words in earlier acts. For instance, in Act I when Lady Capulet asks her daughter "How stands your disposition to be married?" Juliet replies that she is not interested; however, after her mother makes an argument for Paris as a suitor, the complaisant Juliet dutifully replies that although she is not interested, she will obey and fulfill her mother's wishes:
I'll look to like, if looking liking move,
But no more deep will I endart mine eye
Than your consent gives strength to make it fly. (1.3.101-103)
Also in Act I, after Juliet has met Romeo, she treats Nurse as a confidant, asking her "What is yond gentleman...going out of door?" (1.5. 125)
Now, in Act IV, Juliet's demeanor is much different. So, since she has secretly married Romeo and her mother now informs her that she must marry Paris, Juliet is in a quandary. Of course, the Nurse offers her no comfort, either, as she suggests that Juliet go ahead and marry Paris since Romeo is banished and will not return. Besides, she tells Juliet, "Romeo's a dishclout to him" (3.5.230). In love with her husband, Juliet responds to this insult of Nurse's with anger,
Ancient damnation! Oh, most wicked fiend
Is it more sin to wish me thus forsworn
Or to dispraise my lord with that same tongue (3.5.246-248)
Therefore, when Juliet goes to Friar Laurence and agrees to take a potion that will make her seem dead, she acts deceptively, but her actions are done out of desperation. For, Juliet feels that she cannot marry Paris because she is already married, and she cannot tell her parents because the Montagues are enemies of the Capulet family. Furthermore, she deceives the Nurse because she cannot trust her anymore since her conversation with her in Scene 5 of Act III.