"Nothing is so beneficial as true knowledge of ourselves, which produces a wholesome self-contempt.  Always think kindly of others while holding yourself as nothing:  this is true wisdom and leads to perfection.  If you see another commit a grievous sin, or whose faults are flagrant, do not regard yourself as better, for you do not know what you would do if similarly tempted.  You are in good disposition now, but you do not know how long you will persevere in it.  Always keep in mind that all are frail, but none so frail as yourself."

(The Imitation of Christ, Book One, Chapter Two)