In lines 157 to 163 of William Shakespeare's play "Romeo and Juliet," the nurse tells Romeo that he must not lead Juliet on or lie to her, as it is a "weak" thing to do. She says this would be "gross behavior" because of Juliet's young age.
In this scene, Juliet has sent the nurse to Romeo to find out what Romeo's intentions are. Does he plan to marry Juliet? The nurse opens by giving Romeo a warning against leading Juliet on or lying to her. She says not to "lead her [Juliet] into a fool's paradise" and not to "deal double with her." The first warning, not to "lead her into a fool's paradise," means that Romeo must not promise Juliet anything that he won't be able to give her. The second, not to "deal double with her," means that the nurse expects Romeo to be honest with Juliet, perhaps warning him to be faithful to Juliet.
The nurse says that dishonest behavior would be "gross" and "weak dealing" because Juliet is so young. These things show us how protective the nurse is over Juliet. They also emphasize how young Juliet is, and how ironic the situation between Romeo and Juliet is. Their families are feuding, so the nurse must have a healthy distrust to begin with. Perhaps this is why she delivers this opinionated speech before even launching into discussion of what she came to Romeo for.