stay away from sin. The Christian outlook was that everybody has the ability to refrain from sin, and people who do sin are just being lazy or weak. Shakespeare, as well as a number of other poets, though, was aware that on occasion an emotion could become so powerful that it would overthrow a person's reason and cause that person to act irrationally, wildly, and even madly. In Portia's lines above the wordbrainrefers to the rational side of man. Through his reason mankind creates rules and laws that are sensible and logical, but such laws are cold (unemotional) decrees. When the emotions (indicatedbythe wordtemper) become too strong or hot, they ignore or break (or leap over) the cold rules and laws ofsociety.
Portia (Shakespeare actually) adds another complex metaphor to emphasize this idea. She personifies the emotions as a mad or wild youth who, like a rabbit, jumps over and thus avoids the laws and rules of reason or “good counsel” (lines 17-18). Further, reason is personified as a “cripple” because he is physically unable to stop the wild youth. Even during the age of Shakespeare there existed the concept of the rebellious youth who felt compelled to ignore and break the rules of society. And even during the age of Shakespeare all people occasionally experienced strong and even violent emotions that caused them to act irrationally or even madly.