Imam Khomeini sheds the light on the matter in his famous book of "an exposition on Forty Hadith" as following:
Similarly, the forces of passion are implanted in human nature in such a way that even if he is made an absolute monarch of a state, he will be attracted towards another state, which he cannot get, and he will try to pounce on it with all the force he can muster.
This power is also ever increasing. Anyone who has any doubt is advised to examine his own self and other human beings belonging to the classes of poor, rich and powerful; he will agree with me.
It is obvious that man is always allured by something, which he does not own.
This is the human nature as conceived by various great Islamic thinkers and holy men, especially one should refer to a great master of divinity, Mirza Muhammad ‘Ali Shahabadi.
Anyhow, even if man attains his goals, for how long can he be benefited from them? How long his youthful years are to continue?
When the spring of youth fades out and the autumn of his life sets in, his heart has no more a zest for mirth and joy, his organs lose their vitality and those activities lose their relish.
His eyes dim, his hearing is impaired, his sense of touch and other senses and faculties weaken.
Ability to get pleasure declines or is completely lost. Then hosts of ailments make him an easy prey.
His digestive, assimilative and excretory system fails, and his respiratory system cannot perform it: function properly. Nothing but deep sighs, displeasure, regret and remorse are left to accompany him.