in act 3 there are several turn of events that turn the story of romeo and Juliet into a tragedy. In scene 5 lord capulet makes a drastic decision, how does this complicate the plot?

The plot is the story and/or the events that are occurring, so to complicate a plot would mean that an event occurs that throws off how the story has been proceeding. Therefore, as you read, how did Capulet's decision throw off or change the way the story was going? Had he not made this decision, how would the story of proceeded or stayed the same. How did his decision cause a tragedy (or complication) ?