Since Romeo was on the "rebound" from Rosaline, any pretty girl would probably have caused Romeo's heart to skip a beat. However, in speaking to Juliet, a member of his family's enemy, his heart not only skips a beat but he also loses his ability to be reasonable and logical. Of course, Juliet does not know that Romeo is trying to get over another girl, so she does not know the possible genesis of Romeo's "love" for her. They both come into this relationship with different "baggage" of sorts, but since they don't really have any meaningful conversations, they do not know what the other is truly thinking. So, what starts as an innocent meeting at a party ends with disastrous results.