'If it seems to you that you know a great deal and have wide experience in many fields, yet remember that there are matters of which you are ignorant. So do not become conceited, but confess your ignorance. Why do you wish to esteem yourself above others, when there are many who are wise and more perfect in the Law of God? If you desire to know or learn anything, then take delight in being unknown and unregarded.
A true understanding and humble estimate of oneself is the highest and most valuable of all lessons. To take no account of oneself, but always to think well and highly of others is the highest wisdom and perfection. Should you see another person openly doing evil, or carrying out a wicked purpose, do not on that account consider yourself better than him, for you cannot tell how long you will remain in a state of grace. We are all frail; consider none more frail than yourself.'
Thomas à Kempis, The Imitation of Christ, p.29.