There is an old saying that opposites attract--that for every yin there is a yang.  Yet, there also exists the popular notion that extreme feelings often lead to extreme endings.  Throughout Romeo and Juliet, William Shakespeare’s repeated use of antithesis helps foreshadow the idea that things will not work out well for the two young lovers, Romeo and Juliet.  This idea is significant because it teaches the audience that loving in moderation is often safer than being swept away by passion.

Some consequence yet hanging in the stars

Shall bitterly begin his fearful date

With this night's revels, and expire the term

Of a despisèd life closed in my breast

By some vile forfeit of untimely death."

1.4.113-118

Being in night, all this is but a dream,

Too flattering sweet to be substantial."

2.2.146-148