It is those who are subject to the demon of arrogance who especially suffer in this way; because, as their hearts are no longer continually occupied with impure thoughts, they are prone to the passion of pride. And in order to be convinced of the truth of what has been said, when they have achieved a certain measure of holy quiet, let them discreetly examine themselves. Then they will certainly find that some thought is concealed in the depth of their heart like a snake in dung, suggesting to them that they have made some progress in purity of heart by their own effort and zeal. Poor wretches! They do not think of what was said: ‘What hast thou that thou didst not receive as a free gift, either from God, or by the co-operation and prayers of others?’ And so let them look to their own affairs, and let them cast out of their heart with all speed the snake mentioned above, killing it by much humility, so that when they have got rid of it they may in time be stripped of their clothing of skin and as chaste children sing to the Lord the triumph song of purity; if only, when they are stripped, they do not find themselves naked of that humility and freedom from malice which is natural to children.
—St. John Climacus, The Ladder of Divine Ascent