Lord and Lady Capulet
One's opinion should not be ignored by a higher figurehead.
Act 1, Scene 3
Lady Capulet decides to let Juliet make the choice to wed Paris or not. During their exchange of ideas, Lady Capulet asks, "'Speak briefly. Can you accept Paris, love?'" Juliet replies, "I will look to like if looking liking move.'" This is important because Juliet's mother is allowing her to decide for herself, rather than have an arranged marrige.
Act 3, Scene 4
Lord Capulet thinks that Juliet is sad because of the death of her cousin, Tybalt, rather than the banishment of Romeo from Verona. He feels that marrying Paris will make his daughter happy again, so he forces Juliet to marry Paris. This makes matters even worse. Lord Capulet says to Paris, "'Well get gone. A Thursday it be then....Prepare her, wife, against this wedding day.'" Lord Capulet's decision is that Juliet will marry Paris on Thursday.
Act 3, Scene 4
After Lord Capulet and Lady Capulet tell their daughter about her wedding plans, unknowingly that she was not sad because of the death of her cousin, but that she was married to Romeo. When telling Paris, Lord Capulet says, "'Things have fall'n out, sir, so unluckily that we've had no time to move our daughter, look you...'". Juliet should have told her father, and/or her father should not force her into things that she has no interest in. Both sides of the story are to blame for this misunderstanding.
Act 5, Scene 3
Romeo and Juliet's family rivalry ultimately caused their death. If Juliet would have told her father about Romeo, maybe he would have understood. Maybe he would not have. Nobody knows. Out of fear of losing Romeo, she neglected to tell her father because he would never let her see Romeo again just because of his last name. At the children's funeral, Friar Lawrence says "'As rich shall Romeo's by his lady lie, poor sacrifices of our emmity.""