The message found in Act 3, Scene 1 particularly pertains to impulsiveness. To be impulsive is to be influenced by rash emotions rather than by the rational mind. Both Mercutio and Romeo show a great deal of impulsiveness, which leads to violence and death.
Mercutio shows impulsiveness in the very beginning of the scene. Rational, peace-loving Benvolio tries to persuade Mercutio to get off of the street, warning that should they meet any Capulets they "shall not scape a brawl," but he refuses to listen to reason (III.i.3). Had Mercutio listened, they would not have run into Tybalt, and even Romeo might have been spared seeing Tybalt; the fight would have never taken place; and, lives would have been spared. The second time when Mercutio shows impulsiveness in this scene is when he becomes angered by Romeo's attempt to pacify Tybalt, resulting in Mercutio answering Tybalt's challenge to a duel rather than Romeo. Had Mercutio not given way to his rash, impulsive anger, his life would have been spared, showing us that impulsiveness leads to violence, which in turn can lead to death.
Romeo shows equal impulsiveness when he makes the decision to revenge himself on Tybalt for Mercutio's death. After stabbing Mercutio, Tybalt actually immediately flees the scene but then comes back, which we can gather from Benvolio's line, "Here comes the furious Tybalt back again" (122). Had Romeo been using his rational senses as his guide rather than his irrational, impulsive emotions, he too would have fled the scene and left Tybalt to be dealt with by the prince's law. Romeo had no need to kill Tybalt himself because Tybalt was already doomed to die at the hands of the law for killing Mercutio. Romeo's impulsive decision led to not only Tybalt's death but indirectly to his own death as well as Juliet's, showing us again that impulsiveness leads to both violence and death.