Imam Ali (AS) said, Indeed there is a piece of flesh that has been placed inside this human being which is the most amazing thing in him, and that is his heart; it has sources of wisdom and things contrary to it. If hope enters it, covetousness humiliates it and if covetousness increases in it then greed destroys it. If despair takes control over it, grief kills it. If anger comes over it, its rage intensifies. If it is blessed with pleasure, it forgets precaution. If it is overcome by fear, it becomes preoccupied with caution. If peace prevails around it, it becomes neglectful. If a hardship befalls it, impatience disgraces it. If it gains wealth, affluence makes it oppressive. If it faces indigence, distress overtakes it. If hunger attacks it, weakness disables it. If its eating increases, the heaviness of his stomach pains it. Thus every curtailment is harmful to it and every excess is injurious to it.