From Thomas a Kempis’ Imitation of Christ:
Do not think yourself better than others lest, perhaps, you be accounted worse before God Who knows what is in man. Do not take pride in your good deeds, for God’s judgments differ from those of men and what pleases them often displeases Him. If there is good in you, see more good in others, so that you may remain humble. It does no harm to esteem yourself less than anyone else, but it is very harmful to think yourself better than even one. The humble live in continuous peace, while in the hearts of the proud are envy and frequent anger.
When a man desires a thing too much, he at once becomes ill at ease. A proud and avaricious man never rests, whereas he who is poor and humble of heart lives in a world of peace. An unmortified man is quickly tempted and overcome in small, trifling evils; his spirit is weak, in a measure carnal and inclined to sensual things; he can hardly abstain from earthly desires. Hence it makes him sad to forego them; he is quick to anger if reproved. Yet if he satisfies his desires, remorse of conscience overwhelms him because he followed his passions and they did not lead to the peace he sought.
True peace of heart, then, is found in resisting passions, not in satisfying them. There is no peace in the carnal man, in the man given to vain attractions, but there is peace in the fervent and spiritual man.
[resources: Imitation of Christ]