These are taken from the sayings of Ali bin abi Talib (ra/as) in Nahij Al Balaghah (translations):
More wonderful than man himself is that part of his body which is connected with his trunk with muscles. It is his brain (mind). Look what good and bad tendencies arise from it. On the one hand it holds treasures of know- ledge and wisdom and on the other it is found to harbour very ugly desires. If a man sees even a tiny gleam of success, then greed forces him to humiliate himself. If he gives way to avarice, then inordinate desires ruin him, if he is disappointed, then despondency almost kills him. If he is excited, then he loses temper and gets angry. If he is pleased, then he gives up precaution. Sudden fear makes him dull and nervous, and he is unable to think and find a way out of the situation. During the times of peace and prosperity he becomes careless and unmindful of the future. If he acquires wealth, then he becomes haughty and arrogant. If he is plunged in distress, then his agitation, impatience and nervousness disgrace him. 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. In short every kind of loss and gain makes his mind unbalanced.
No wealth is more useful than intelligence and wisdom; no solitude is more horrible than when people avoid you on account of your vanity and conceit or when you wrongly consider yourself above everybody to confide and consult; no eminence is more exalting than piety; no companion can prove more useful than politeness; no heritage is better than culture; no leader is superior to Divine Guidance; no deal is more profitable than good deeds; no profit is greater than Divine Reward; no abstinence is better than to restrain one’s mind from doubts (about religion); no virtue is better than refraining from prohibited deeds; no knowledge is superior to deep thinking and prudence; no worship or prayers are more sacred than fulfillment of obligations and duties, no religious faith is loftier than feeling ashamed of doing wrong and bearing calamities patiently; no eminence is greater than to adopt humbleness; no exaltation is superior to knowledge; nothing is more respectable than forgiveness and forbearance; no support and defense are stronger than consultation.