In Romeo and Juliet, Friar Lawrence's warning to Romeo that "violent delights have violent ends" introduces the paradoxical themes of love and violence.
Friar Lawrence's warning to Romeo that impulsive behavior and violent love can end badly goes unheeded as the priest urges the young man to "love moderately" so that love will last. Romeo ignores the conventions of his time in which a man would request permission from the father before marrying his daughter. Instead, Romeo exhorts the friar to secretly perform marriage rites for him and Juliet. When the friar realizes that Romeo and Juliet will act on their love with or without his help, he agrees to marry them.
Juliet ignores convention and acts impulsively as well. In fact, she even ignores the rules of convention that she has followed earlier, having promised her mother that she would consider Paris as suitor:
I'll look to like, if looking liking move
But no more deep will I endart mine eye
Than you consent gives strength to make it fly (1.3.99-101)
Now as she awaits the Nurse to return from her meeting with Romeo, Juliet is impatient and hasty in her actions:
Now is the sun upon the highmost hillOf this day’s journey, and from nine till twelveIs three long hours, yet she is not come.Had she affections and warm youthful blood,She would be as swift in motion as a ball. (2.5.9-13)
Even though he has agreed to marry Romeo to Juliet not more than a day after the young couple meet, Friar Lawrence preaches patience and moderation to Romeo at the beginning of Act II, Scene 6. The Friar warns that something which happens swiftly may seem too good to be true and can eventually lead to complications. The Friar says,
These violent delights have violent endsAnd in their triumph die, like fire and powder,Which, as they kiss, consume. The sweetest honeyIs loathsome in his own deliciousnessAnd in the taste confounds the appetite.Therefore love moderately. Long love doth so.Too swift arrives as tardy as too slow.