"But He fashioned him in due proportion, and breathed into him something of His spirit. And He gave you (the faculties of) hearing and sight and feeling (and understanding): little thanks do ye give!"
 

(Holy Qur'an (Yusufali) 32:009)

"More wonderful than man himself is that part of his body which is connected with his trunk with muscles. It is his mind. Look what good and bad tendencies it is a source of:

1. On one hand it holds treasures of knowledge and wisdom, and on the other it is found to harbour very ugly desires.
2. If a man sees a tiny gleam of success then greed forces him to humiliate himself.
3. If he gives way to avarice (greed, materialism), then inordinate (excessive) desires ruin him;
4. If he is disappointed then despondency almost kills him.
5. If he is excited then he loses temper and gets angry.
6. If he is pleased then he gives up his precaution.
7. Sudden fear makes him dull and nervous and he is unable to think and find a way out of the situation.
8. During times of peace and prosperity, he becomes careless and unmindful of future.
9. If he acquires wealth then he becomes haughty and arrogant.
10. If he is plunged in distress then his agitation, impatience and nervousness disgrace him.
11. If he is overtaken by poverty then he finds himself in a very sad plight; hunger makes him weak and over-feeding harms him equally.
12. In short, every kind of loss and gain unbalances his mind."
     
    

(Nahjul Balagha: Sermons, letters and saying of Hazrat Ali (Second American edition, 1981), Sayings of Hazrat Ali 107, p. 284)