How does Romeo and Juliet offer valuable insight into human behavior?

This play can teach its audience about the terrible lengths to which we will often go for love, for pride, or for power.  It isn't just about the teenagers who fall in love at first sight; although their story has value, too.  The play also focuses on the terrible, but human, behavior of the Capulets and Montagues in terms of their feud, a grudge that is so long-standing that no one even seems to discuss...

This play can teach its audience about the terrible lengths to which we will often go for love, for pride, or for power.  It isn't just about the teenagers who fall in love at first sight; although their story has value, too.  The play also focuses on the terrible, but human, behavior of the Capulets and Montagues in terms of their feud, a grudge that is so long-standing that no one even seems to discuss the disagreement with which it began.  For family pride then, the feud continues, and it is responsible, ultimately, for Tybalt's death, as well as the deaths of Mercutio, Paris, Romeo, and Juliet.  Were it not for the ridiculous and proud fight between the family patriarchs, Tybalt would not have felt dishonored by Romeo's presence at the party.  He would not have challenged Romeo, and thus Mercutio would not have become involved (which he does, also, for honor).  Romeo would not be banished for slaying Tybalt, he would not have killed Paris and Juliet's tomb, and the tragedy could not have unfolded as it did.  

Further, Lord Capulet's proud insistence on his daughter's absolute obedience when he orders her to marry Count Paris denies her speech, opens a gulf between Juliet and her parents, and makes her desperate.  His need to rule over her, and his unwillingness to hear her at all, leads, ultimately, to her death as well as Romeo's and Paris's.  

In the end, most of adults behave immaturely and selfishly.  They think only of themselves and their own pride,  They have little care or concern for others, and they drive their children to desperate lengths.  In terms of human behavior, we see that humans will most often act in order to retain or acquire power or to preserve their pride.  We see how the practice of such selfish behavior leads only to tragedy and pain.  From this play, we learn that we often fail to consider all the possible repercussions of our selfish behaviors and how they can, and often do, return to plague us in the end.