In both Shakespeare's Romeo and Juliet and William Golding's Lord of the Flies, due to the character trait of hotheadedness, characters regress to acting on instincts rather than on rational thought; furthermore, their instincts drive them to act upon wild, passionate emotions.
In Romeo and Juliet, Tybalt serves as one example of a character who acts based on the primal instincts of wild, passionate emotions as a result of his hotheaded, fiery temper. One example can be seen in even the very first scene. The moment the two Capulet servants, Sampson and Gregory, break out into a fight with the two Montague servants, Abraham and Balthasar, Benvolio rushes out to break up the fight, saying, "Part, fools! / Put up your swords; you know not what you do," and according to the stage direction, "beats down their swords" with his own (I.i.50-51). Yet, Tybalt sees Benvolio with his sword drawn and, rather than rationally assessing the situation, as a result of his fiery temper, is driven by his instincts to conclude that Benvolio has started a fight with the servants and rushes out with his own sword to join the fray. Had he had a calmer, more rational temper, Tybalt would have used his rational thoughts to recognized what Benvolio was really doing and joined him in trying to make peace.
Similarly, in Lord of the Flies, the boys on the island are driven by instincts to act on passionate emotions rather than on rational thought. Such instincts lead to heinous acts, including the murders of Simon and Piggy, and it is primarily Jack, an equally hotheaded and even arrogant boy, who leads the boys to act upon their wild, instinctive emotions.